Set up RSpec for testing with GOV.UK conventions

 - Add `rspec-rails` and `govuk_test` gems
 - Set up RSpec configuration with sensible initial defaults and GOV.UK
   conventions from Developer Docs

.gitignore

@@ -17,3 +17,9 @@
 /tmp/pids/*
 !/tmp/pids/
 !/tmp/pids/.keep
+
+# RSpec run persistence (for e.g. --only-failures)
+spec/examples.txt
+
+# Simplecov
+/coverage/*

.rspec

@@ -0,0 +1 @@
+--require spec_helper

Gemfile

@@ -11,6 +11,12 @@ gem "activesupport", RAILS_GEMS_VERSION
 
 gem "puma", "~> 5.0"
 
+group :test do
+  gem "simplecov", require: false
+end
+
 group :development, :test do
   gem "debug", platforms: %i[ mri mingw x64_mingw ]
+  gem "govuk_test"
+  gem "rspec-rails"
 end

Gemfile.lock

@@ -21,13 +21,32 @@ GEM
       i18n (>= 1.6, < 2)
       minitest (>= 5.1)
       tzinfo (~> 2.0)
+    addressable (2.8.5)
+      public_suffix (>= 2.0.2, < 6.0)
+    brakeman (6.0.1)
     builder (3.2.4)
+    capybara (3.39.2)
+      addressable
+      matrix
+      mini_mime (>= 0.1.3)
+      nokogiri (~> 1.8)
+      rack (>= 1.6.0)
+      rack-test (>= 0.6.3)
+      regexp_parser (>= 1.5, < 3.0)
+      xpath (~> 3.2)
     concurrent-ruby (1.2.2)
     crass (1.0.6)
     debug (1.8.0)
       irb (>= 1.5.0)
       reline (>= 0.3.1)
+    diff-lcs (1.5.0)
+    docile (1.4.0)
     erubi (1.12.0)
+    govuk_test (3.0.1)
+      brakeman (>= 5.0.2)
+      capybara (>= 3.36)
+      puma
+      selenium-webdriver (>= 4.0)
     i18n (1.14.1)
       concurrent-ruby (~> 1.0)
     io-console (0.6.0)
@@ -36,11 +55,14 @@ GEM
     loofah (2.21.3)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
+    matrix (0.4.2)
     method_source (1.0.0)
+    mini_mime (1.1.5)
     minitest (5.19.0)
     nio4r (2.5.9)
     nokogiri (1.15.4-aarch64-linux)
       racc (~> 1.4)
+    public_suffix (5.0.3)
     puma (5.6.7)
       nio4r (~> 2.0)
     racc (1.7.1)
@@ -62,11 +84,44 @@ GEM
       thor (~> 1.0)
       zeitwerk (~> 2.5)
     rake (13.0.6)
+    regexp_parser (2.8.1)
     reline (0.3.8)
       io-console (~> 0.5)
+    rexml (3.2.6)
+    rspec-core (3.12.2)
+      rspec-support (~> 3.12.0)
+    rspec-expectations (3.12.3)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-mocks (3.12.6)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-rails (6.0.3)
+      actionpack (>= 6.1)
+      activesupport (>= 6.1)
+      railties (>= 6.1)
+      rspec-core (~> 3.12)
+      rspec-expectations (~> 3.12)
+      rspec-mocks (~> 3.12)
+      rspec-support (~> 3.12)
+    rspec-support (3.12.1)
+    rubyzip (2.3.2)
+    selenium-webdriver (4.11.0)
+      rexml (~> 3.2, >= 3.2.5)
+      rubyzip (>= 1.2.2, < 3.0)
+      websocket (~> 1.0)
+    simplecov (0.22.0)
+      docile (~> 1.1)
+      simplecov-html (~> 0.11)
+      simplecov_json_formatter (~> 0.1)
+    simplecov-html (0.12.3)
+    simplecov_json_formatter (0.1.4)
     thor (1.2.2)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    websocket (1.2.9)
+    xpath (3.2.0)
+      nokogiri (~> 1.8)
     zeitwerk (2.6.11)
 
 PLATFORMS
@@ -77,8 +132,11 @@ DEPENDENCIES
   activemodel (= 7.0.7.2)
   activesupport (= 7.0.7.2)
   debug
+  govuk_test
   puma (~> 5.0)
   railties (= 7.0.7.2)
+  rspec-rails
+  simplecov
 
 RUBY VERSION
    ruby 3.2.2p53

spec/spec_helper.rb

@@ -0,0 +1,32 @@
+ENV["RAILS_ENV"] ||= "test"
+
+require "simplecov"
+SimpleCov.start "rails"
+
+require File.expand_path("../../config/environment", __FILE__)
+require "rspec/rails"
+
+Dir[Rails.root.join("spec/support/**/*.rb")].each { |f| require f }
+GovukTest.configure
+
+# See https://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  config.default_formatter = "doc" if config.files_to_run.one?
+  config.disable_monkey_patching!
+  config.example_status_persistence_file_path = "spec/examples.txt"
+  config.expose_dsl_globally = false
+  config.infer_spec_type_from_file_location!
+  config.profile_examples = 10
+  config.shared_context_metadata_behavior = :apply_to_host_groups # Preempting v4 default
+
+  config.order = :random
+  Kernel.srand config.seed
+
+  config.expect_with :rspec do |expectations|
+    expectations.include_chain_clauses_in_custom_matcher_descriptions = true # Preempting v4 default
+  end
+
+  config.mock_with :rspec do |mocks|
+    mocks.verify_partial_doubles = true # Preempting v4 default
+  end
+end