diff --git a/.gitattributes b/.gitattributes
index 1a31373..7a6aaab 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,6 +1,9 @@
 .github
 .gitattributes export-ignore
+.github export-ignore
 .gitignore export-ignore
+docker-compose.yml export-ignore
+Dockerfile export-ignore
 Makefile export-ignore
-phpunit.xml.dist export-ignore
+phpunit.xml export-ignore
 tests/ export-ignore
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ce665de..96968b1 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -7,13 +7,12 @@ on:
 jobs:
   phpunit:
     name: phpunit
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         php-version:
-        - "5.6"
-        - "7.0"
-        - "7.4"
+        - "7.3"
+        - "8.1"
     steps:
     - name: Checkout
       uses: actions/checkout@v2
@@ -40,7 +39,7 @@ jobs:
       run: make test-coveralls
 
     - name: Upload code coverage
-      if: ${{ matrix.php-version == '5.6' }}
+      if: ${{ matrix.php-version == '7.3' }}
       env:
         COVERALLS_REPO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       run: |
diff --git a/.gitignore b/.gitignore
index 073e37a..4edb3d9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+.phpunit.result.cache
 build
 composer.lock
 vendor
diff --git a/MIGRATION.md b/MIGRATION.md
new file mode 100644
index 0000000..c4b5adf
--- /dev/null
+++ b/MIGRATION.md
@@ -0,0 +1,23 @@
+# Migration
+
+## v1.x to v2.x
+
+### New Requirements
+
+Requires PHP 7.3+
+
+### New features
+
+None
+
+### Backward Incompatible Changes
+
+None
+
+### Deprecated Features
+
+None
+
+### Other Changes
+
+None
diff --git a/Makefile b/Makefile
index f500375..8d148f4 100644
--- a/Makefile
+++ b/Makefile
@@ -8,6 +8,8 @@ PHPUNIT = vendor/bin/phpunit
 vendor:
 	@composer install
 
+# testing
+
 .PHONY: test-dependencies
 test-dependencies: vendor
 
@@ -18,19 +20,19 @@ test: test-dependencies
 .PHONY: test-coverage
 test-coverage: test-dependencies
 	@mkdir -p build/coverage
-	@$(PHPUNIT) --coverage-html build/coverage
+	@XDEBUG_MODE=coverage $(PHPUNIT) --coverage-html build/coverage
 
 .PHONY: test-coveralls
 test-coveralls: test-dependencies
 	@mkdir -p build/logs
-	@$(PHPUNIT) --coverage-clover build/logs/clover.xml
+	@XDEBUG_MODE=coverage $(PHPUNIT) --coverage-clover build/logs/clover.xml
 
-.PHONY: test-container-56
-test-container-56:
-	@docker-compose run --rm app56 sh
+.PHONY: test-container-73
+test-container-73:
+	@docker-compose run --rm app73 sh
 	@docker-compose down
 
-.PHONY: test-container-74
-test-container-74:
-	@docker-compose run --rm app74 sh
+.PHONY: test-container-81
+test-container-81:
+	@docker-compose run --rm app81 sh
 	@docker-compose down
diff --git a/README.md b/README.md
index 2227eb3..152f085 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,12 @@ year, quarter and more has been made especially easy. Also, all instances can be
 
 
 
+#### Installation
+
+```bash
+composer require icanboogie/datetime
+```
+
 
 
 ### Usage
@@ -343,36 +349,6 @@ echo $date->localize('fr')->as_medium;        // 5 mai 2015 23:13:05
 
 
 
-## Installation
-
-The recommended way to install this package is through [Composer](https://getcomposer.org/):
-
-```
-$ composer require icanboogie/datetime
-```
-
-The package [icanboogie/common](https://github.com/ICanBoogie/Common) is suggested to
-provide finer exceptions, such as [PropertyNotDefined][] and [PropertyNotWritable][].
-If the package is not included, `RunTimeException` instances are thrown instead.
-
-
-
-## Documentation
-
-The package is documented as part of the [ICanBoogie](http://icanboogie.org/) framework
-[documentation][]. The documentation for the package and its
-dependencies can be generated with the `make doc` command. The documentation is generated in
-the `build/docs` directory using [ApiGen](http://apigen.org/). The package directory can later by
-cleaned with the `make clean` command.
-
-The following classes are documented:
-
-- [DateTime][]
-- [TimeZone][]
-- [TimeZoneLocation][]
-
-
-
 ## Continuous Integration
 
 The project is continuously tested by [GitHub actions](https://github.com/ICanBoogie/DateTime/actions).
@@ -395,9 +371,6 @@ Please see [CONTRIBUTING](CONTRIBUTING.md) for details.
 
 [ICanBoogie/CLDR]:            https://github.com/ICanBoogie/CLDR
 [JsonSerializable interface]: http://php.net/manual/en/class.jsonserializable.php
-[documentation]:              http://api.icanboogie.org/datetime/latest/
-[DateTime]:                   http://api.icanboogie.org/datetime/latest/class-ICanBoogie.DateTime.html
-[TimeZone]:                   http://api.icanboogie.org/datetime/latest/class-ICanBoogie.TimeZone.html
-[TimeZoneLocation]:           http://api.icanboogie.org/datetime/latest/class-ICanBoogie.TimeZoneLocation.html
-[PropertyNotDefined]:         http://api.icanboogie.org/common/1.2/class-ICanBoogie.PropertyNotDefined.html
-[PropertyNotWritable]:        http://api.icanboogie.org/common/1.2/class-ICanBoogie.PropertyNotWritable.html
+[DateTime]:                   lib/DateTime.php
+[TimeZone]:                   lib/TimeZone.php
+[TimeZoneLocation]:           lib/TimeZoneLocation.php
diff --git a/composer.json b/composer.json
index 136b752..5c19f46 100644
--- a/composer.json
+++ b/composer.json
@@ -9,7 +9,7 @@
 		{
 			"name": "Olivier Laviale",
 			"email": "olivier.laviale@gmail.com",
-			"homepage": "https://olvlvl.com",
+			"homepage": "https://olvlvl.com/",
 			"role" : "Developer"
 		}
 	],
@@ -17,19 +17,27 @@
 		"issues": "https://github.com/ICanBoogie/DateTime/issues",
 		"source": "https://github.com/ICanBoogie/DateTime"
 	},
+	"config": {
+		"sort-packages": true
+	},
 	"require": {
-		"php": ">=5.6.0"
+		"php": ">=7.3"
 	},
 	"require-dev": {
-		"icanboogie/common": "^1.2",
-		"phpunit/phpunit": "^5.6"
+		"icanboogie/common": "^2.0",
+		"phpunit/phpunit": "^9.5"
 	},
 	"suggest": {
 		"icanboogie/common": "Allows finer exceptions to be thrown"
 	},
 	"autoload": {
 		"psr-4": {
-			"ICanBoogie\\": "lib/"
+			"ICanBoogie\\": "lib"
+		}
+	},
+	"autoload-dev": {
+		"psr-4": {
+			"Test\\ICanBoogie\\": "tests"
 		}
 	}
 }
diff --git a/docker-compose.yaml b/docker-compose.yaml
index 190188e..953abf0 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -1,22 +1,22 @@
 ---
 version: "3.0"
 services:
-  app56:
+  app73:
     build:
       context: .
       args:
-        PHP_VERSION: 5.6
+        PHP_VERSION: 7.3
     environment:
       PHP_IDE_CONFIG: "serverName=icanboogie-datetime"
     volumes:
       - .:/app:delegated
       - ~/.composer:/root/.composer:delegated
     working_dir: /app
-  app74:
+  app81:
     build:
       context: .
       args:
-        PHP_VERSION: 7.4
+        PHP_VERSION: 8.1
     environment:
       PHP_IDE_CONFIG: "serverName=icanboogie-datetime"
     volumes:
diff --git a/lib/DateTime.php b/lib/DateTime.php
index bf3d096..f194158 100644
--- a/lib/DateTime.php
+++ b/lib/DateTime.php
@@ -11,6 +11,9 @@
 
 namespace ICanBoogie;
 
+use DateTimeZone;
+use RuntimeException;
+
 /**
  * Representation of a date and time.
  *
@@ -169,38 +172,28 @@ class DateTime extends \DateTime implements \JsonSerializable
 	 * We redefine the constant to make sure that the cookie uses a valid pattern.
 	 *
 	 * @see http://grokbase.com/t/php/php-bugs/111xynxd6m/php-bug-bug-53879-new-datetime-createfromformat-fails-to-parse-cookie-expiration-date
-	 *
-	 * @var string
 	 */
-	const COOKIE = 'l, d-M-Y H:i:s T';
+	public const COOKIE = 'l, d-M-Y H:i:s T';
 
 	/**
 	 * DB (example: 2013-02-03 20:59:03)
-	 *
-	 * @var string
 	 */
-	const DB = 'Y-m-d H:i:s';
+	public const DB = 'Y-m-d H:i:s';
 
 	/**
 	 * Number (example: 20130203205903)
-	 *
-	 * @var string
 	 */
-	const NUMBER = 'YmdHis';
+	public const NUMBER = 'YmdHis';
 
 	/**
 	 * Date (example: 2013-02-03)
-	 *
-	 * @var string
 	 */
-	const DATE = 'Y-m-d';
+	public const DATE = 'Y-m-d';
 
 	/**
 	 * Time (example: 20:59:03)
-	 *
-	 * @var string
 	 */
-	const TIME = 'H:i:s';
+	public const TIME = 'H:i:s';
 
 	/**
 	 * Callable used to create localized instances.
@@ -225,10 +218,8 @@ class DateTime extends \DateTime implements \JsonSerializable
 	 * @param mixed $source
 	 * @param mixed $timezone The time zone to use to create the time. The value is ignored if the
 	 * source is an instance of {@link \DateTime}.
-	 *
-	 * @return DateTime
 	 */
-	static public function from($source, $timezone = null)
+	static public function from($source, $timezone = null): self
 	{
 		if ($source instanceof static)
 		{
@@ -249,10 +240,8 @@ static public function from($source, $timezone = null)
 	 * **Note:** Subsequent calls return equal times, event if they are minutes apart. _now_
 	 * actually refers to the `REQUEST_TIME` or, if it is now available, to the first time
 	 * the method was invoked.
-	 *
-	 * @return static
 	 */
-	static public function now()
+	static public function now(): self
 	{
 		static $now;
 
@@ -268,10 +257,8 @@ static public function now()
 	 * Returns an instance with the current local time and the local time zone.
 	 *
 	 * **Note:** Subsequent calls may return different times.
-	 *
-	 * @return static
 	 */
-	static public function right_now()
+	static public function right_now(): self
 	{
 		return new static;
 	}
@@ -293,12 +280,12 @@ static public function right_now()
 	 * $d->zone->name;                    // "Asia/Tokio"
 	 * </pre>
 	 *
-	 * @param \DateTimeZone|string $timezone The time zone in which the empty date is created.
+	 * @param DateTimeZone|string $timezone The time zone in which the empty date is created.
 	 * Defaults to "UTC".
 	 *
 	 * @return DateTime
 	 */
-	static public function none($timezone = 'utc')
+	static public function none($timezone = 'utc'): self
 	{
 		return new static('0000-00-00', $timezone);
 	}
@@ -317,22 +304,16 @@ static public function none($timezone = 'utc')
 	 * new DateTime;
 	 * </pre>
 	 *
-	 * @param string $time Defaults to "now".
-	 * @param \DateTimeZone|string|null $timezone
+	 * @param DateTimeZone|string|null $timezone
 	 */
-	public function __construct($time = 'now', $timezone = null)
+	public function __construct(string $time = 'now', $timezone = null)
 	{
 		if (is_string($timezone))
 		{
-			$timezone = new \DateTimeZone($timezone);
+			$timezone = new DateTimeZone($timezone);
 		}
 
-		#
-		# PHP 5.3.3 considers null $timezone as an error and will complain that it is not
-		# a \DateTimeZone instance.
-		#
-
-		$timezone === null ? parent::__construct($time) : parent::__construct($time, $timezone);
+		parent::__construct($time, $timezone);
 	}
 
 	/**
@@ -404,8 +385,16 @@ public function __get($property)
 				$time->setTime(0, 0, 0);
 				return $time;
 
-			/*
+			/**
 			 * days
+			 *
+			 * @uses get_monday
+			 * @uses get_tuesday
+			 * @uses get_wednesday
+			 * @uses get_thursday
+			 * @uses get_friday
+			 * @uses get_saturday
+			 * @uses get_sunday
 			 */
 			case 'monday':
 			case 'tuesday':
@@ -434,22 +423,20 @@ public function __get($property)
 				return $transitions[0]['isdst'];
 		}
 
-		if (class_exists('ICanBoogie\PropertyNotDefined'))
+		if (class_exists(PropertyNotDefined::class))
 		{
 			throw new PropertyNotDefined([ $property, $this ]);
 		}
 		else
 		{
-			throw new \RuntimeException("Property is not defined: $property.");
+			throw new RuntimeException("Property is not defined: $property.");
 		}
 	}
 
 	/**
 	 * Returns Monday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_monday()
+	private function get_monday(): self
 	{
 		$time = clone $this;
 		$day = $time->weekday;
@@ -466,60 +453,48 @@ protected function get_monday()
 
 	/**
 	 * Returns Tuesday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_tuesday()
+	private function get_tuesday(): self
 	{
 		return $this->monday->modify('+1 day');
 	}
 
 	/**
 	 * Returns Wednesday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_wednesday()
+	private function get_wednesday(): self
 	{
 		return $this->monday->modify('+2 day');
 	}
 
 	/**
 	 * Returns Thursday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_thursday()
+	private function get_thursday(): self
 	{
 		return $this->monday->modify('+3 day');
 	}
 
 	/**
 	 * Returns Friday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_friday()
+	private function get_friday(): self
 	{
 		return $this->monday->modify('+4 day');
 	}
 
 	/**
 	 * Returns Saturday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_saturday()
+	private function get_saturday(): self
 	{
 		return $this->monday->modify('+5 day');
 	}
 
 	/**
 	 * Returns Sunday of the week.
-	 *
-	 * @return DateTime
 	 */
-	protected function get_sunday()
+	private function get_sunday(): self
 	{
 		$time = clone $this;
 		$day = $time->weekday;
@@ -543,10 +518,12 @@ protected function get_sunday()
 	 *
 	 * @inheritdoc
 	 */
-	public function __set($property, $value)
+	public function __set($property, $value): void
 	{
-		static $readonly = [ 'quarter', 'week', 'year_day', 'weekday',
-		'tomorrow', 'yesterday', 'utc', 'local' ];
+		static $readonly = [
+			'quarter', 'week', 'year_day', 'weekday',
+			'tomorrow', 'yesterday', 'utc', 'local'
+		];
 
 		switch ($property)
 		{
@@ -570,23 +547,23 @@ public function __set($property, $value)
 
 		if (strpos($property, 'is_') === 0 || strpos($property, 'as_') === 0 || in_array($property, $readonly) || method_exists($this, 'get_' . $property))
 		{
-			if (class_exists('ICanBoogie\PropertyNotWritable'))
+			if (class_exists(PropertyNotWritable::class))
 			{
 				throw new PropertyNotWritable([ $property, $this ]);
 			}
 			else
 			{
-				throw new \RuntimeException("Property is not writeable: $property.");
+				throw new RuntimeException("Property is not writeable: $property.");
 			}
 		}
 
-		if (class_exists('ICanBoogie\PropertyNotDefined'))
+		if (class_exists(PropertyNotDefined::class))
 		{
 			throw new PropertyNotDefined([ $property, $this ]);
 		}
 		else
 		{
-			throw new \RuntimeException("Property is not defined: $property.");
+			throw new RuntimeException("Property is not defined: $property.");
 		}
 	}
 
@@ -634,17 +611,15 @@ public function __call($method, $arguments)
 	 * @return string The instance rendered as an {@link ISO8601} string, or an empty string if the
 	 * datetime is empty.
 	 */
-	public function __toString()
+	public function __toString(): string
 	{
 		return $this->is_empty ? "" : $this->as_iso8601;
 	}
 
 	/**
 	 * Returns a {@link ISO8601} representation of the instance.
-	 *
-	 * @return string
 	 */
-	public function jsonSerialize()
+	public function jsonSerialize(): string
 	{
 		return (string) $this;
 	}
@@ -657,16 +632,16 @@ public function jsonSerialize()
 	 *
 	 * @inheritdoc
 	 */
-	public function setTimezone($timezone)
+	public function setTimezone($timezone): self
 	{
 		if ($timezone === 'local')
 		{
 			$timezone = date_default_timezone_get();
 		}
 
-		if (!$timezone instanceof \DateTimeZone)
+		if (!$timezone instanceof DateTimeZone)
 		{
-			$timezone = new \DateTimeZone($timezone);
+			$timezone = new DateTimeZone($timezone);
 		}
 
 		return parent::setTimezone($timezone);
@@ -689,14 +664,12 @@ public function setTimezone($timezone)
 	 * $time->change([ 'year' => 2000, 'second' => 0 ]);
 	 * </pre>
 	 *
-	 * @param array $options
+	 * @param array{ year: int, month: int, day: int, hour: int, minute: int, second: int, timezone: string } $options
 	 * @param bool $cascade If `true`, time options (`hour`, `minute`, `second`) reset
 	 * cascading, so if only the hour is passed, then minute and second is set to 0. If the hour
 	 * and minute is passed, then second is set to 0.
-	 *
-	 * @return DateTime
 	 */
-	public function change(array $options, $cascade=false)
+	public function change(array $options, bool $cascade = false): self
 	{
 		static $default_options = [
 
@@ -766,12 +739,12 @@ public function change(array $options, $cascade=false)
 	/**
 	 * Instantiate a new instance with changes properties.
 	 *
-	 * @param array $options
-	 * @param bool $cascade
-	 *
-	 * @return DateTime
+	 * @param array{ year: int, month: int, day: int, hour: int, minute: int, second: int, timezone: string } $options
+	 * @param bool $cascade If `true`, time options (`hour`, `minute`, `second`) reset
+	 * cascading, so if only the hour is passed, then minute and second is set to 0. If the hour
+	 * and minute is passed, then second is set to 0.
 	 */
-	public function with(array $options, $cascade = false)
+	public function with(array $options, bool $cascade = false): self
 	{
 		$dt = clone $this;
 
@@ -787,7 +760,7 @@ public function with(array $options, $cascade = false)
 	 *
 	 * @inheritdoc
 	 */
-	public function format($format)
+	public function format($format): string
 	{
 		if (($format == self::DATE || $format == self::DB) && $this->is_empty)
 		{
@@ -800,19 +773,17 @@ public function format($format)
 	/**
 	 * Returns a localized instance.
 	 *
-	 * @param string $locale
-	 *
 	 * @return mixed
 	 *
-	 * @throws \RuntimeException if {@link $localizer} is not defined.
+	 * @throws RuntimeException if {@link $localizer} is not defined.
 	 */
-	public function localize($locale = 'en')
+	public function localize(string $locale = 'en')
 	{
 		$localizer = self::$localizer;
 
 		if (!$localizer)
 		{
-			throw new \RuntimeException("Localizer is not defined yet.");
+			throw new RuntimeException("Localizer is not defined yet.");
 		}
 
 		return $localizer($this, $locale);
diff --git a/lib/TimeZone.php b/lib/TimeZone.php
index b9daf12..62a3877 100644
--- a/lib/TimeZone.php
+++ b/lib/TimeZone.php
@@ -45,10 +45,8 @@ class TimeZone extends \DateTimeZone
 	 * the same instance.
 	 *
 	 * @param mixed $source Source of the timezone.
-	 *
-	 * @return TimeZone
 	 */
-	static public function from($source)
+	static public function from($source): self
 	{
 		if ($source instanceof self)
 		{
@@ -87,10 +85,8 @@ static public function from($source)
 
 	/**
 	 * Initializes the {@link $name} property.
-	 *
-	 * @param string $timezone
 	 */
-	public function __construct($timezone)
+	public function __construct(string $timezone)
 	{
 		parent::__construct($timezone);
 
@@ -111,7 +107,7 @@ public function __construct($timezone)
 	 *
 	 * @inheritdoc
 	 */
-	public function __get($property)
+	public function __get(string $property)
 	{
 		switch ($property)
 		{
@@ -140,7 +136,7 @@ public function __get($property)
 				return $this->getOffset($utc_time);
 		}
 
-		if (class_exists('ICanBoogie\PropertyNotDefined'))
+		if (class_exists(PropertyNotDefined::class))
 		{
 			throw new PropertyNotDefined([ $property, $this ]);
 		}
@@ -152,10 +148,8 @@ public function __get($property)
 
 	/**
 	 * Returns the name of the timezone.
-	 *
-	 * @return string
 	 */
-	public function __toString()
+	public function __toString(): string
 	{
 		return $this->name;
 	}
diff --git a/lib/TimeZoneLocation.php b/lib/TimeZoneLocation.php
index 3f188b6..a50c9c2 100644
--- a/lib/TimeZoneLocation.php
+++ b/lib/TimeZoneLocation.php
@@ -11,6 +11,8 @@
 
 namespace ICanBoogie;
 
+use RuntimeException;
+
 /**
  * Representation of a time zone location.
  *
@@ -41,12 +43,8 @@ class TimeZoneLocation
 
 	/**
 	 * Creates an instance from a {@link \DateTimeZone} instance.
-	 *
-	 * @param \DateTimeZone $zone
-	 *
-	 * @return \ICanBoogie\TimeZoneLocation
 	 */
-	static public function from(\DateTimeZone $zone)
+	static public function from(\DateTimeZone $zone): self
 	{
 		$hash = spl_object_hash($zone);
 
@@ -75,8 +73,6 @@ public function __construct(array $location)
 	 * {@link $comments} properties.
 	 *
 	 * @throws PropertyNotDefined in attempt to get an unsupported property.
-	 *
-	 * @inheritdoc
 	 */
 	public function __get($property)
 	{
@@ -85,13 +81,13 @@ public function __get($property)
 			return $this->location[$property];
 		}
 
-		if (class_exists('ICanBoogie\PropertyNotDefined'))
+		if (class_exists(PropertyNotDefined::class))
 		{
 			throw new PropertyNotDefined([ $property, $this ]);
 		}
 		else
 		{
-			throw new \RuntimeException("Property is not defined: $property.");
+			throw new RuntimeException("Property is not defined: $property.");
 		}
 	}
 
@@ -102,13 +98,13 @@ public function __get($property)
 	 */
 	public function __set($property, $value)
 	{
-		if (class_exists('ICanBoogie\PropertyNotWritable'))
+		if (class_exists(PropertyNotWritable::class))
 		{
 			throw new PropertyNotWritable([ $property, $this ]);
 		}
 		else
 		{
-			throw new \RuntimeException("Property is not writable: $property.");
+			throw new RuntimeException("Property is not writable: $property.");
 		}
 	}
 
@@ -117,8 +113,8 @@ public function __set($property, $value)
 	 *
 	 * @return string
 	 */
-	public function __toString()
+	public function __toString(): string
 	{
-		return "{$this->country_code},{$this->latitude},{$this->longitude}";
+		return "$this->country_code,$this->latitude,$this->longitude";
 	}
 }
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..7b5140a
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd" colors="true"
+		 bootstrap="./vendor/autoload.php">
+	<coverage>
+		<include>
+			<directory suffix=".php">./lib</directory>
+		</include>
+	</coverage>
+	<testsuites>
+		<testsuite name="ICanBoogie/DateTime">
+			<directory>./tests</directory>
+		</testsuite>
+	</testsuites>
+</phpunit>
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
deleted file mode 100644
index 18113bc..0000000
--- a/phpunit.xml.dist
+++ /dev/null
@@ -1,21 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit
-		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-		xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/5.7/phpunit.xsd"
-		backupGlobals="false"
-		colors="true"
-		bootstrap="./vendor/autoload.php"
->
-	<testsuites>
-		<testsuite name="ICanBoogie/DateTime">
-			<directory>./tests</directory>
-		</testsuite>
-	</testsuites>
-
-	<filter>
-		<whitelist processUncoveredFilesFromWhitelist="true">
-			<directory suffix=".php">./lib</directory>
-		</whitelist>
-	</filter>
-</phpunit>
diff --git a/tests/DateTimeTest.php b/tests/DateTimeTest.php
index 9fb9204..7b13ae9 100644
--- a/tests/DateTimeTest.php
+++ b/tests/DateTimeTest.php
@@ -9,19 +9,56 @@
  * file that was distributed with this source code.
  */
 
-namespace Tests\ICanBoogie;
+namespace Test\ICanBoogie;
 
 use ICanBoogie\DateTime;
-use ICanBoogie\DateTimeTest\MyDateTime;
+use ICanBoogie\PropertyNotDefined;
+use ICanBoogie\PropertyNotWritable;
 use PHPUnit\Framework\TestCase;
+use Test\ICanBoogie\DateTimeTest\MyDateTime;
+use function array_map;
+use function preg_split;
+use function trim;
 
-class DateTimeTest extends TestCase
+final class DateTimeTest extends TestCase
 {
-	protected function setUp()
+	protected function setUp(): void
 	{
 		date_default_timezone_set('Europe/Paris');
 	}
 
+	/**
+	 * @dataProvider provide_readonly
+	 */
+	public function test_readonly(string $property): void
+	{
+		$d = DateTime::now();
+
+		$this->expectExceptionMessage("The property `$property` for object of class `ICanBoogie\DateTime` is not writable.");
+		$this->expectException(PropertyNotWritable::class);
+		$d->{ $property } = null;
+	}
+
+	public function provide_readonly(): array
+	{
+		$properties = <<<EOT
+		quarter week weekday year_day 
+		is_monday is_tuesday is_wednesday is_thursday is_friday is_saturday is_sunday
+		is_today is_past is_future is_empty 
+		tomorrow yesterday 
+		monday tuesday wednesday thursday friday saturday sunday
+		utc is_utc
+		local is_local
+		is_dst
+		as_atom as_cookie as_iso8601 as_rfc822 as_rfc850 as_rfc1036 as_rfc1123 as_rfc2822 as_rfc3339 as_rss as_w3c as_db as_number as_date as_time
+		EOT;
+
+		return array_map(
+			function ($v) { return [ $v ]; },
+			preg_split("/\s+/", trim($properties))
+		);
+	}
+
 	public function test_now()
 	{
 		$d = DateTime::now();
@@ -133,7 +170,7 @@ public function test_change()
 		$this->assertEquals('2001-01-01 01:01:01', $d->as_db);
 	}
 
-	public function provider_test_change_cascade()
+	public function provider_test_change_cascade(): array
 	{
 		return [
 			['2001-01-01 01:02:00', [ 'minute' => 2 ]],
@@ -146,7 +183,7 @@ public function provider_test_change_cascade()
 		];
 	}
 
-	public function test_change_on_timezone_option()
+	public function test_change_on_timezone_option(): void
 	{
 		$expectedTimezone = 'Asia/Taipei';
 		$now = new DateTime();
@@ -164,7 +201,7 @@ public function test_change_on_timezone_option()
 	/**
 	 * @dataProvider provider_test_change_cascade
 	 */
-	public function test_change_cascade($expected_datetime, $change_format)
+	public function test_change_cascade($expected_datetime, $change_format): void
 	{
 		$datetime = '2001-01-01 01:01:01';
 
@@ -172,7 +209,7 @@ public function test_change_cascade($expected_datetime, $change_format)
 		$this->assertEquals($expected_datetime, $d->change($change_format, true)->as_db);
 	}
 
-	public function test_with()
+	public function test_with(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$e = $d->with([ 'year' => 2015, 'month' => 5, 'day' => 5 ]);
@@ -184,7 +221,7 @@ public function test_with()
 		$this->assertEquals('2015-05-05 01:01:01', $e->as_db);
 	}
 
-	public function provider_test_get_year()
+	public function provider_test_get_year(): array
 	{
 		return [
 			['2012-12-16 15:00:00', 2012],
@@ -196,20 +233,20 @@ public function provider_test_get_year()
 	/**
 	 * @dataProvider provider_test_get_year
 	 */
-	public function test_get_year($datetime, $expected)
+	public function test_get_year($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->year);
 	}
 
-	public function test_set_year()
+	public function test_set_year(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->year = 2009;
 		$this->assertEquals('2009-01-01 01:01:01', $d->as_db);
 	}
 
-	public function provider_test_get_quarter()
+	public function provider_test_get_quarter(): array
 	{
 		return [
 			['2012-01-16 15:00:00', 1],
@@ -230,23 +267,13 @@ public function provider_test_get_quarter()
 	/**
 	 * @dataProvider provider_test_get_quarter
 	 */
-	public function test_get_quarter($datetime, $expected)
+	public function test_get_quarter($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->quarter);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `quarter` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_quarter()
-	{
-		$d = DateTime::now();
-		$d->quarter = true;
-	}
-
-	public function provider_test_get_month()
+	public function provider_test_get_month(): array
 	{
 		return [
 			['2012-01-16 15:00:00', 1],
@@ -258,20 +285,20 @@ public function provider_test_get_month()
 	/**
 	 * @dataProvider provider_test_get_month
 	 */
-	public function test_get_month($datetime, $expected)
+	public function test_get_month($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->month);
 	}
 
-	public function test_set_month()
+	public function test_set_month(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->month = 9;
 		$this->assertEquals('2001-09-01 01:01:01', $d->as_db);
 	}
 
-	public function provider_test_get_week()
+	public function provider_test_get_week(): array
 	{
 		return [
 			['2012-01-01 15:00:00', 52],
@@ -282,23 +309,13 @@ public function provider_test_get_week()
 	/**
 	 * @dataProvider provider_test_get_week
 	 */
-	public function test_get_week($datetime, $expected)
+	public function test_get_week($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->week);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `week` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_week()
-	{
-		$d = DateTime::now();
-		$d->week = true;
-	}
-
-	public function provider_test_get_year_day()
+	public function provider_test_get_year_day(): array
 	{
 		return [
 			['2012-01-01 15:00:00', 1],
@@ -309,23 +326,13 @@ public function provider_test_get_year_day()
 	/**
 	 * @dataProvider provider_test_get_year_day
 	 */
-	public function test_get_year_day($datetime, $expected)
+	public function test_get_year_day($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->year_day);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `year_day` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_year_day()
-	{
-		$d = DateTime::now();
-		$d->year_day = true;
-	}
-
-	public function provider_test_get_weekday()
+	public function provider_test_get_weekday(): array
 	{
 		return [
 			['2012-12-17 15:00:00', 1],
@@ -342,23 +349,13 @@ public function provider_test_get_weekday()
 	 * Sunday must be 7, Monday must be 1.
 	 * @dataProvider provider_test_get_weekday
 	 */
-	public function test_get_weekday($datetime, $expected)
+	public function test_get_weekday($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->weekday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `weekday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_weekday()
-	{
-		$d = DateTime::now();
-		$d->weekday = true;
-	}
-
-	public function provider_test_get_day()
+	public function provider_test_get_day(): array
 	{
 		return [
 			['2012-12-16 15:00:00', 16],
@@ -370,59 +367,59 @@ public function provider_test_get_day()
 	/**
 	 * @dataProvider provider_test_get_day
 	 */
-	public function test_get_day($datetime, $expected)
+	public function test_get_day($datetime, $expected): void
 	{
 		$d = new DateTime($datetime);
 		$this->assertEquals($expected, $d->day);
 	}
 
-	public function test_set_day()
+	public function test_set_day(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->day = 9;
 		$this->assertEquals('2001-01-09 01:01:01', $d->as_db);
 	}
 
-	public function test_get_hour()
+	public function test_get_hour(): void
 	{
 		$d = new DateTime('2013-01-01 01:23:45');
 		$this->assertEquals(1, $d->hour);
 	}
 
-	public function test_set_hour()
+	public function test_set_hour(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->hour = 9;
 		$this->assertEquals('2001-01-01 09:01:01', $d->as_db);
 	}
 
-	public function test_get_minute()
+	public function test_get_minute(): void
 	{
 		$d = new DateTime('2013-01-01 01:23:45');
 		$this->assertEquals(23, $d->minute);
 	}
 
-	public function test_set_minute()
+	public function test_set_minute(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->minute = 9;
 		$this->assertEquals('2001-01-01 01:09:01', $d->as_db);
 	}
 
-	public function test_get_second()
+	public function test_get_second(): void
 	{
 		$d = new DateTime('2013-01-01 01:23:45');
 		$this->assertEquals(45, $d->second);
 	}
 
-	public function test_set_second()
+	public function test_set_second(): void
 	{
 		$d = new DateTime('2001-01-01 01:01:01');
 		$d->second = 9;
 		$this->assertEquals('2001-01-01 01:01:09', $d->as_db);
 	}
 
-	public function test_get_is_monday()
+	public function test_get_is_monday(): void
 	{
 		$d = new DateTime('2013-02-04 21:00:00', 'utc');
 		$this->assertTrue($d->is_monday);
@@ -434,17 +431,7 @@ public function test_get_is_monday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_monday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_monday()
-	{
-		$d = new DateTime('2013-02-04 21:00:00', 'utc');
-		$d->is_monday = true;
-	}
-
-	public function test_get_is_tuesday()
+	public function test_get_is_tuesday(): void
 	{
 		$d = new DateTime('2013-02-05 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -456,17 +443,7 @@ public function test_get_is_tuesday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_tuesday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_tuesday()
-	{
-		$d = new DateTime('2013-02-05 21:00:00', 'utc');
-		$d->is_tuesday = true;
-	}
-
-	public function test_get_is_wednesday()
+	public function test_get_is_wednesday(): void
 	{
 		$d = new DateTime('2013-02-06 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -478,17 +455,7 @@ public function test_get_is_wednesday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_wednesday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_wednesday()
-	{
-		$d = new DateTime('2013-02-06 21:00:00', 'utc');
-		$d->is_wednesday = true;
-	}
-
-	public function test_get_is_thursday()
+	public function test_get_is_thursday(): void
 	{
 		$d = new DateTime('2013-02-07 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -500,17 +467,7 @@ public function test_get_is_thursday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_thursday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_thursday()
-	{
-		$d = new DateTime('2013-02-07 21:00:00', 'utc');
-		$d->is_thursday = true;
-	}
-
-	public function test_get_is_friday()
+	public function test_get_is_friday(): void
 	{
 		$d = new DateTime('2013-02-08 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -522,17 +479,7 @@ public function test_get_is_friday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_friday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_friday()
-	{
-		$d = new DateTime('2013-02-08 21:00:00', 'utc');
-		$d->is_friday = true;
-	}
-
-	public function test_get_is_saturday()
+	public function test_get_is_saturday(): void
 	{
 		$d = new DateTime('2013-02-09 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -544,17 +491,7 @@ public function test_get_is_saturday()
 		$this->assertFalse($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_saturday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_saturday()
-	{
-		$d = new DateTime('2013-02-09 21:00:00', 'utc');
-		$d->is_saturday = true;
-	}
-
-	public function test_get_is_sunday()
+	public function test_get_is_sunday(): void
 	{
 		$d = new DateTime('2013-02-10 21:00:00', 'utc');
 		$this->assertFalse($d->is_monday);
@@ -566,17 +503,7 @@ public function test_get_is_sunday()
 		$this->assertTrue($d->is_sunday);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_sunday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_sunday()
-	{
-		$d = new DateTime('2013-02-10 21:00:00', 'utc');
-		$d->is_sunday = true;
-	}
-
-	public function test_get_is_today()
+	public function test_get_is_today(): void
 	{
 		$d = DateTime::now();
 		$d->zone = 'Asia/Tokyo';
@@ -585,17 +512,7 @@ public function test_get_is_today()
 		$this->assertFalse($d->yesterday->is_today);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_today` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_today()
-	{
-		$d = DateTime::now();
-		$d->is_today = true;
-	}
-
-	public function test_get_is_past()
+	public function test_get_is_past(): void
 	{
 		$d = DateTime::now();
 		$d->zone = 'Asia/Tokyo';
@@ -605,17 +522,7 @@ public function test_get_is_past()
 		$this->assertFalse($d->is_past);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_past` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_past()
-	{
-		$d = DateTime::now();
-		$d->is_past = true;
-	}
-
-	public function test_get_is_future()
+	public function test_get_is_future(): void
 	{
 		$d = DateTime::now();
 		$d->zone = 'Asia/Tokyo';
@@ -625,16 +532,6 @@ public function test_get_is_future()
 		$this->assertTrue($d->is_future);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_future` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_future()
-	{
-		$d = DateTime::now();
-		$d->is_future = true;
-	}
-
 	public function test_get_is_empty()
 	{
 		$d = DateTime::none();
@@ -649,74 +546,28 @@ public function test_get_is_empty()
 		$this->assertFalse($d->is_empty);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_empty` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_empty()
-	{
-		DateTime::now()->is_empty = true;
-	}
-
 	public function test_get_tomorrow()
 	{
 		$d = new DateTime('2013-02-10 21:21:21', 'utc');
 		$this->assertEquals('2013-02-11 00:00:00', $d->tomorrow->as_db);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `tomorrow` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_tomorrow()
-	{
-		$d = DateTime::now();
-		$d->tomorrow = true;
-	}
-
 	public function test_get_yesterday()
 	{
 		$d = new DateTime('2013-02-10 21:21:21', 'utc');
 		$this->assertEquals('2013-02-09 00:00:00', $d->yesterday->as_db);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `yesterday` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_yesterday()
-	{
-		$d = DateTime::now();
-		$d->yesterday = true;
-	}
-
-	/**
-	 * @dataProvider provide_writeonly_property
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessageReg The property `\w+` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_writeonly_property($property)
-	{
-		DateTime::now()->$property = null;
-	}
-
-	public function provide_writeonly_property()
-	{
-		$properties = 'monday|tuesday|wednesday|thursday|friday|saturday|sunday';
-
-		return array_map(function($v) { return (array) $v; }, explode('|', $properties));
-	}
-
 	/**
 	 * @dataProvider provide_test_day_instance
 	 */
-	public function test_day_instance($date, $expected, $day)
+	public function test_day_instance($date, $expected, $day): void
 	{
 		$d = new DateTime($date);
 		$this->assertEquals($expected, $d->$day->as_db);
 	}
 
-	public function provide_test_day_instance()
+	public function provide_test_day_instance(): array
 	{
 		return [
 
@@ -835,21 +686,21 @@ public function provide_test_day_instance()
 		];
 	}
 
-	public function test_far_past()
+	public function test_far_past(): void
 	{
 		$d = new DateTime('-4712-12-07 12:06:46');
 		$this->assertEquals(-4712, $d->year);
 		$this->assertEquals('-4712-12-07 12:06:46', $d->as_db);
 	}
 
-	public function test_far_future()
+	public function test_far_future(): void
 	{
 		$d = new DateTime('4712-12-07 12:06:46');
 		$this->assertEquals(4712, $d->year);
 		$this->assertEquals('4712-12-07 12:06:46', $d->as_db);
 	}
 
-	public function test_get_utc()
+	public function test_get_utc(): void
 	{
 		$d = new DateTime('2013-03-06 18:00:00', 'Europe/Paris');
 		$utc = $d->utc;
@@ -858,17 +709,7 @@ public function test_get_utc()
 		$this->assertEquals('2013-03-06 17:00:00', $utc->as_db);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `utc` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_utc()
-	{
-		$d = DateTime::now();
-		$d->utc = null;
-	}
-
-	public function test_get_is_utc()
+	public function test_get_is_utc(): void
 	{
 		$d = DateTime::now();
 		$d->zone = 'Asia/Tokyo';
@@ -877,16 +718,6 @@ public function test_get_is_utc()
 		$this->assertTrue($d->is_utc);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_utc` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_utc()
-	{
-		$d = DateTime::now();
-		$d->is_utc = true;
-	}
-
 	public function test_get_local()
 	{
 		$d = new DateTime('2013-03-06 17:00:00', 'UTC');
@@ -896,16 +727,6 @@ public function test_get_local()
 		$this->assertEquals('2013-03-06 18:00:00', $local->as_db);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `local` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_local()
-	{
-		$d = DateTime::now();
-		$d->local = true;
-	}
-
 	public function test_get_is_local()
 	{
 		$d = DateTime::now();
@@ -915,16 +736,6 @@ public function test_get_is_local()
 		$this->assertTrue($d->is_local);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_local` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_local()
-	{
-		$d = DateTime::now();
-		$d->is_local = true;
-	}
-
 	public function test_get_is_dst()
 	{
 		$d = new DateTime('2013-02-03 21:00:00');
@@ -933,16 +744,6 @@ public function test_get_is_dst()
 		$this->assertTrue($d->is_dst);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `is_dst` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_is_dst()
-	{
-		$d = DateTime::now();
-		$d->is_dst = true;
-	}
-
 	public function test_format()
 	{
 		$empty = DateTime::none();
@@ -955,28 +756,18 @@ public function test_format()
 	 * Predefined formats
 	 */
 
-	public function test_format_as_atom()
+	public function test_format_as_atom(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::ATOM), $now->format_as_atom());
 	}
 
-	public function test_get_as_atom()
+	public function test_get_as_atom(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::ATOM), $now->as_atom);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_atom` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_atom()
-	{
-		$d = DateTime::now();
-		$d->as_atom = true;
-	}
-
 	public function test_format_as_cookie()
 	{
 		$now = DateTime::now();
@@ -992,251 +783,151 @@ public function test_get_as_cookie()
 		$this->assertEquals("Monday, 04-Nov-2013 20:21:22 UTC", $date->as_cookie);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_cookie` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_cookie()
-	{
-		$d = DateTime::now();
-		$d->as_cookie = true;
-	}
-
-	public function test_format_as_iso8601()
+	public function test_format_as_iso8601(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::ISO8601), $now->format_as_iso8601());
 	}
 
-	public function test_format_as_iso8601_utc()
+	public function test_format_as_iso8601_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'Z', $now->format(DateTime::ISO8601)), $now->format_as_iso8601());
 	}
 
-	public function test_get_as_iso8601()
+	public function test_get_as_iso8601(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::ISO8601), $now->as_iso8601);
 	}
 
-	public function test_as_iso8601_utc()
+	public function test_as_iso8601_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'Z', $now->format(DateTime::ISO8601)), $now->as_iso8601);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_iso8601` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_iso8601()
-	{
-		$d = DateTime::now();
-		$d->as_iso8601 = true;
-	}
-
-	public function test_format_as_rfc822()
+	public function test_format_as_rfc822(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC822), $now->format_as_rfc822());
 	}
 
-	public function test_format_as_rfc822_utc()
+	public function test_format_as_rfc822_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'GMT', $now->format(DateTime::RFC822)), $now->format_as_rfc822());
 	}
 
-	public function test_get_as_rfc822()
+	public function test_get_as_rfc822(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC822), $now->as_rfc822);
 	}
 
-	public function test_get_as_rfc822_utc()
+	public function test_get_as_rfc822_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'GMT', $now->format(DateTime::RFC822)), $now->as_rfc822);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc822` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc822()
-	{
-		$d = DateTime::now();
-		$d->as_rfc822 = true;
-	}
-
-	public function test_format_as_rfc850()
+	public function test_format_as_rfc850(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC850), $now->format_as_rfc850());
 	}
 
-	public function test_get_as_rfc850()
+	public function test_get_as_rfc850(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC850), $now->as_rfc850);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc850` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc850()
-	{
-		$d = DateTime::now();
-		$d->as_rfc850 = true;
-	}
-
-	public function test_format_as_rfc1036()
+	public function test_format_as_rfc1036(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC1036), $now->format_as_rfc1036());
 	}
 
-	public function test_get_as_rfc1036()
+	public function test_get_as_rfc1036(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC1036), $now->as_rfc1036);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc1036` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc1036()
-	{
-		$d = DateTime::now();
-		$d->as_rfc1036 = true;
-	}
-
-	public function test_format_as_rfc1123()
+	public function test_format_as_rfc1123(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC1123), $now->format_as_rfc1123());
 	}
 
-	public function test_format_as_rfc1123_utc()
+	public function test_format_as_rfc1123_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'GMT', $now->format(DateTime::RFC1123)), $now->format_as_rfc1123());
 	}
 
-	public function test_get_as_rfc1123()
+	public function test_get_as_rfc1123(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC1123), $now->as_rfc1123);
 	}
 
-	public function test_get_as_rfc1123_utc()
+	public function test_get_as_rfc1123_utc(): void
 	{
 		$now = DateTime::now()->utc;
 		$this->assertEquals(str_replace('+0000', 'GMT', $now->format(DateTime::RFC1123)), $now->as_rfc1123);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc1123` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc1123()
-	{
-		$d = DateTime::now();
-		$d->as_rfc1123 = true;
-	}
-
-	public function test_format_as_rfc2822()
+	public function test_format_as_rfc2822(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC2822), $now->format_as_rfc2822());
 	}
 
-	public function test_get_as_rfc2822()
+	public function test_get_as_rfc2822(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC2822), $now->as_rfc2822);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc2822` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc2822()
-	{
-		$d = DateTime::now();
-		$d->as_rfc2822 = true;
-	}
-
-	public function test_format_as_rfc3339()
+	public function test_format_as_rfc3339(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC3339), $now->format_as_rfc3339());
 	}
 
-	public function test_get_as_rfc3339()
+	public function test_get_as_rfc3339(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RFC3339), $now->as_rfc3339);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rfc3339` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rfc3339()
-	{
-		$d = DateTime::now();
-		$d->as_rfc3339 = true;
-	}
-
-	public function test_format_as_rss()
+	public function test_format_as_rss(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RSS), $now->format_as_rss());
 	}
 
-	public function test_get_as_rss()
+	public function test_get_as_rss(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::RSS), $now->as_rss);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_rss` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_rss()
-	{
-		$d = DateTime::now();
-		$d->as_rss = true;
-	}
-
-	public function test_format_as_w3c()
+	public function test_format_as_w3c(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::W3C), $now->format_as_w3c());
 	}
 
-	public function test_get_as_w3c()
+	public function test_get_as_w3c(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::W3C), $now->as_w3c);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_w3c` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_w3c()
-	{
-		$d = DateTime::now();
-		$d->as_w3c = true;
-	}
-
-	public function test_format_as_db()
+	public function test_format_as_db(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::DB), $now->format_as_db());
@@ -1244,7 +935,7 @@ public function test_format_as_db()
 		$this->assertEquals('0000-00-00 00:00:00', $empty->format_as_db());
 	}
 
-	public function test_get_as_db()
+	public function test_get_as_db(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::DB), $now->as_db);
@@ -1252,39 +943,19 @@ public function test_get_as_db()
 		$this->assertEquals('0000-00-00 00:00:00', $empty->as_db);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_db` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_db()
-	{
-		$d = DateTime::now();
-		$d->as_db = true;
-	}
-
-	public function test_format_as_number()
+	public function test_format_as_number(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::NUMBER), $now->format_as_number());
 	}
 
-	public function test_get_as_number()
+	public function test_get_as_number(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::NUMBER), $now->as_number);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_number` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_number()
-	{
-		$d = DateTime::now();
-		$d->as_number = true;
-	}
-
-	public function test_format_as_date()
+	public function test_format_as_date(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::DATE), $now->format_as_date());
@@ -1292,7 +963,7 @@ public function test_format_as_date()
 		$this->assertEquals('0000-00-00', $empty->format_as_date());
 	}
 
-	public function test_get_as_date()
+	public function test_get_as_date(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::DATE), $now->as_date);
@@ -1300,39 +971,19 @@ public function test_get_as_date()
 		$this->assertEquals('0000-00-00', $empty->as_date);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_date` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_date()
-	{
-		$d = DateTime::now();
-		$d->as_date = true;
-	}
-
-	public function test_format_as_time()
+	public function test_format_as_time(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::TIME), $now->format_as_time());
 	}
 
-	public function test_get_as_time()
+	public function test_get_as_time(): void
 	{
 		$now = DateTime::now();
 		$this->assertEquals($now->format(DateTime::TIME), $now->as_time);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `as_time` for object of class `ICanBoogie\DateTime` is not writable.
-	 */
-	public function test_set_as_time()
-	{
-		$d = DateTime::now();
-		$d->as_time = true;
-	}
-
-	public function test_compare()
+	public function test_compare(): void
 	{
 		$d1 = DateTime::now();
 		$d2 = DateTime::now();
@@ -1354,42 +1005,42 @@ public function test_compare()
 		$this->assertSame($tomorrow, max($now, $yesterday, $tomorrow));
 	}
 
-	public function test_json_serialize()
+	public function test_json_serialize(): void
 	{
 		$date = new DateTime("2014-10-23 13:50:10", "Europe/Paris");
 		$this->assertEquals('{"date":"2014-10-23T13:50:10+0200"}', json_encode([ 'date' => $date ]));
 	}
 
-	public function test_localize()
+	public function test_localize(): void
 	{
 		$invoked = false;
 		$reference = DateTime::now();
 
 		DateTime::$localizer = function(DateTime $datetime, $locale) use (&$invoked, &$reference) {
 
+			$invoked = true;
 			$this->assertSame($datetime, $reference);
 			$this->assertEquals('fr', $locale);
 
 		};
 
 		$reference->localize('fr');
+
+		$this->assertTrue($invoked);
 	}
 
-	/**
-	 * @expectedException \RuntimeException
-	 * @expectedExceptionMessageReg Undefined property `\w+` for object of class `ICanBoogie\DateTime`.
-	 */
 	public function test_getting_undefined_property_should_throw_exception()
 	{
 		$date = DateTime::now();
 		$property = uniqid();
+		$this->expectException(PropertyNotDefined::class);
+		$this->expectExceptionMessage("Undefined property `$property` for object of class `ICanBoogie\DateTime`.");
 		$date->$property;
 	}
 }
 
-namespace ICanBoogie\DateTimeTest;
+namespace Test\ICanBoogie\DateTimeTest;
 
-class MyDateTime extends \ICanBoogie\DateTime
+final class MyDateTime extends \ICanBoogie\DateTime
 {
-
 }
diff --git a/tests/TimeZoneLocationTest.php b/tests/TimeZoneLocationTest.php
index 81072f2..d5ad980 100644
--- a/tests/TimeZoneLocationTest.php
+++ b/tests/TimeZoneLocationTest.php
@@ -9,154 +9,127 @@
  * file that was distributed with this source code.
  */
 
-namespace Tests\ICanBoogie;
+namespace Test\ICanBoogie;
 
+use DateTimeZone;
+use ICanBoogie\DateTime;
+use ICanBoogie\PropertyNotDefined;
+use ICanBoogie\PropertyNotWritable;
 use ICanBoogie\TimeZoneLocation;
 use PHPUnit\Framework\TestCase;
+use function array_map;
+use function preg_split;
+use function trim;
 
 class TimeZoneLocationTest extends TestCase
 {
-	public function test_from()
-	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = TimeZoneLocation::from($zone);
-
-		$this->assertInstanceOf(TimeZoneLocation::class, $location);
-	}
-
-	public function test_from_cache()
-	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = TimeZoneLocation::from($zone);
-		$cached = TimeZoneLocation::from($zone);
 
-		$this->assertEquals(spl_object_hash($location), spl_object_hash($cached));
-	}
-
-	public function test_location()
-	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = $zone->getLocation();
-		new TimeZoneLocation($location);
-	}
-
-	public function test_get_coutry_code()
+	/**
+	 * @dataProvider provide_readonly
+	 */
+	public function test_readonly(string $property): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$this->assertEquals($location['country_code'], $instance->country_code);
+		$this->expectExceptionMessage("The property `$property` for object of class `ICanBoogie\TimeZoneLocation` is not writable.");
+		$this->expectException(PropertyNotWritable::class);
+		$instance->$property = null;
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `country_code` for object of class `ICanBoogie\TimeZoneLocation` is not writable.
-	 */
-	public function test_set_country_code()
+	public function provide_readonly(): array
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = $zone->getLocation();
-		$instance = new TimeZoneLocation($location);
-
-		$instance->country_code = true;
+		$properties = <<<EOT
+		country_code
+		latitude
+		longitude
+		comments
+		unsupported_property
+		EOT;
+
+		return array_map(
+			function ($v) { return [ $v ]; },
+			preg_split("/\s+/", trim($properties))
+		);
 	}
 
-	public function test_get_latitude()
+	public function test_from(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = $zone->getLocation();
-		$instance = new TimeZoneLocation($location);
+		$zone = new DateTimeZone('Europe/Paris');
+		$location = TimeZoneLocation::from($zone);
 
-		$this->assertEquals($location['latitude'], $instance->latitude);
+		$this->assertInstanceOf(TimeZoneLocation::class, $location);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `latitude` for object of class `ICanBoogie\TimeZoneLocation` is not writable.
-	 */
-	public function test_set_latitude()
+	public function test_from_cache(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
-		$location = $zone->getLocation();
-		$instance = new TimeZoneLocation($location);
+		$zone = new DateTimeZone('Europe/Paris');
+		$location = TimeZoneLocation::from($zone);
+		$cached = TimeZoneLocation::from($zone);
 
-		$instance->latitude = true;
+		$this->assertEquals(spl_object_hash($location), spl_object_hash($cached));
 	}
 
-	public function test_get_longitude()
+	public function test_location(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
-		$instance = new TimeZoneLocation($location);
+		$l = new TimeZoneLocation($location);
 
-		$this->assertEquals($location['longitude'], $instance->longitude);
+		$this->assertEquals("FR", $l->country_code);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `longitude` for object of class `ICanBoogie\TimeZoneLocation` is not writable.
-	 */
-	public function test_set_longitude()
+	public function test_get_country_code(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$instance->longitude = true;
+		$this->assertEquals($location['country_code'], $instance->country_code);
 	}
 
-	public function test_get_comments()
+	public function test_get_latitude(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$this->assertEquals($location['comments'], $instance->comments);
+		$this->assertEquals($location['latitude'], $instance->latitude);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `comments` for object of class `ICanBoogie\TimeZoneLocation` is not writable.
-	 */
-	public function test_set_comments()
+	public function test_get_longitude(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$instance->comments = true;
+		$this->assertEquals($location['longitude'], $instance->longitude);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotDefined
-	 * @expectedExceptionMessage Undefined property `you_know_that_i_m_no_good` for object of class `ICanBoogie\TimeZoneLocation`.
-	 */
-	public function test_get_unsupported_property()
+	public function test_get_comments(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$instance->you_know_that_i_m_no_good;
+		$this->assertEquals($location['comments'], $instance->comments);
 	}
 
-	/**
-	 * @expectedException \ICanBoogie\PropertyNotWritable
-	 * @expectedExceptionMessage The property `unsupported_property` for object of class `ICanBoogie\TimeZoneLocation` is not writable.
-	 */
-	public function test_set_unsupported_property()
+	public function test_get_unsupported_property(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
-		$instance->unsupported_property = true;
+		$this->expectExceptionMessage("Undefined property `you_know_that_i_m_no_good` for object of class `ICanBoogie\TimeZoneLocation`.");
+		$this->expectException(PropertyNotDefined::class);
+		$instance->you_know_that_i_m_no_good;
 	}
 
-	public function test_to_string()
+	public function test_to_string(): void
 	{
-		$zone = new \DateTimeZone('Europe/Paris');
+		$zone = new DateTimeZone('Europe/Paris');
 		$location = $zone->getLocation();
 		$instance = new TimeZoneLocation($location);
 
diff --git a/tests/TimeZoneTest.php b/tests/TimeZoneTest.php
index 6102ffa..9ee69b4 100644
--- a/tests/TimeZoneTest.php
+++ b/tests/TimeZoneTest.php
@@ -9,27 +9,28 @@
  * file that was distributed with this source code.
  */
 
-namespace Tests\ICanBoogie;
+namespace Test\ICanBoogie;
 
+use ICanBoogie\PropertyNotDefined;
 use ICanBoogie\TimeZone;
 use ICanBoogie\TimeZoneLocation;
 use PHPUnit\Framework\TestCase;
 
-class TimeZoneTest extends TestCase
+final class TimeZoneTest extends TestCase
 {
-	public function test_get_location()
+	public function test_get_location(): void
 	{
 		$z = new TimeZone('Europe/Paris');
 		$this->assertInstanceOf(TimeZoneLocation::class, $z->location);
 	}
 
-	public function test_get_name()
+	public function test_get_name(): void
 	{
 		$z = new TimeZone('Europe/Paris');
 		$this->assertEquals($z->getName(), $z->name);
 	}
 
-	public function test_get_offset()
+	public function test_get_offset(): void
 	{
 		$z = new TimeZone('Europe/Paris');
 		$utc = new \DateTime('now', new \DateTimeZone('utc'));
@@ -37,7 +38,7 @@ public function test_get_offset()
 		$this->assertEquals($z->getOffset($utc), $z->offset);
 	}
 
-	public function test_utc_case()
+	public function test_utc_case(): void
 	{
 		$this->assertEquals('UTC', TimeZone::from('utc')->name);
 		$this->assertEquals('UTC', TimeZone::from('UTC')->name);
@@ -45,7 +46,7 @@ public function test_utc_case()
 		$this->assertEquals('UTC', (new TimeZone('UTC'))->name);
 	}
 
-	public function test_should_create_from_php_datetimezone()
+	public function test_should_create_from_php_datetimezone(): void
 	{
 		$name = 'Europe/Paris';
 		$z1 = new \DateTimeZone($name);
@@ -54,7 +55,7 @@ public function test_should_create_from_php_datetimezone()
 		$this->assertSame($name, $z2->name);
 	}
 
-	public function test_should_reuse_instance()
+	public function test_should_reuse_instance(): void
 	{
 		$z1 = TimeZone::from('utc');
 		$z2 = TimeZone::from('utc');
@@ -62,7 +63,7 @@ public function test_should_reuse_instance()
 		$this->assertSame($z1, $z2);
 	}
 
-	public function test_should_reuse_timezone()
+	public function test_should_reuse_timezone(): void
 	{
 		$z1 = TimeZone::from('Europe/Paris');
 		$z2 = TimeZone::from($z1);
@@ -70,17 +71,15 @@ public function test_should_reuse_timezone()
 		$this->assertSame($z1, $z2);
 	}
 
-	/**
-	 * @expectedException \RuntimeException
-	 */
-	public function test_getting_undefined_property_should_throw_exception()
+	public function test_getting_undefined_property_should_throw_exception(): void
 	{
 		$property = uniqid();
 		$z1 = TimeZone::from('utc');
+		$this->expectException(PropertyNotDefined::class);
 		$z1->$property;
 	}
 
-	public function test_to_string()
+	public function test_to_string(): void
 	{
 		$name = 'Europe/Paris';
 		$z1 = TimeZone::from($name);