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03-integration-testing.md

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Integration testing

  • testing how different components interact
  • composing interactions

Integration testing

  • Always a good indicator for
    • decoupling
    • correct layer of abstraction

Test matrix

test-matrix

Test matrix - Code smell

  • "overcomplicated code" quadrant
    • wrong layer of abstraction
    • missing encapsulation
  • solution: move logic to domain object

test-matrix2

What should we test?

  • focus on user stories, not on technical details
  • often evokes better design!
  • when testing technical details:
    • focus on happy path
    • bug report: write a test demonstrating the bug; then fix the bug
    • keep techn. tests maintainable!

Test Doubles

  • Mock (spy)
    • emulate outcoming interactions
  • Stub (dummy, fake)
    • emulate incoming interactions

Many modern frameworks don't make this distinction.

test-double

Manually creating Mocks

  • only useful for simple objects
  • time consuming

Mocking frameworks

  • often require interface or virtual methods (C#)
  • focus on methods required in test
  • setup pre conditions
  • verify post conditions

C# Mocking frameworks

NSubstitute

// Arrange
var mailer = Substitute.For<IMailer>(); // <--

var validCustomer = new ValidCustomer();

// We inject an interface to the system-under-test!
// Mocking frameworks can control the behaviour of the injected object!
var sut = new RegistrationService(mailer);

// Act
sut.Register(validCustomer);

// Assert
mailer.Received().Send(); // <--

examples in code