How to use test doubles (spies, stubs, and mocks) effectively in PHPUnit?

Using test doubles (spies, stubs, and mocks) effectively in PHPUnit can greatly enhance the testing capabilities of your code. Here are some guidelines to follow in order to use them effectively:

1. Understand the difference between spies, stubs, and mocks:

   • Spies: These are test doubles that record what methods were called on them, allowing you to inspect the calls afterward. They are useful when you want to observe and verify the behavior of an object.
   • Stubs: These are test doubles that provide canned responses to method calls. They are useful when you want to replace a real object with a test-specific version that behaves predictably for testing.
   • Mocks: These are test doubles that have pre-programmed expectations about what methods will be called and in what order. They are useful when you want to set up specific behaviors and verify that the expected interactions occur.

2. Use the appropriate test double for your specific needs:

   • If you need to observe and verify the behavior of an object, use a spy.
   • If you need to replace a real object with a predictable version for testing, use a stub.
   • If you need to set up specific behaviors and verify the expected interactions, use a mock.

3. Use PHPUnit's built-in methods to create test doubles:

   • PHPUnit provides methods like createStub(), createMock(), and createConfiguredMock() to create stubs and mocks. Use these methods to create test doubles in your unit tests.

4. Configure the test double's behavior:

   • After creating a stub or mock, you can use PHPUnit's methods like willReturn(), willReturnMap(), will($this->returnCallback()), etc., to configure the behavior of the test double. This allows you to specify what the test double should do when specific methods are called.

5. Verify the expected interactions:

   • Use PHPUnit's built-in assertion methods like expects($this->once()), expects($this->atLeastOnce()), expects($this->never()), etc., to verify that specific methods are called on a mock object and how many times those methods are called.

6. Make use of PHPUnit's PHPUnit\Framework\MockObject\Matcher classes:

   • PHPUnit provides various Matcher classes like PHPUnit\Framework\MockObject\Matcher\InvokedCount, PHPUnit\Framework\MockObject\Matcher\AnyInvokedCount, etc., to perform more specific and advanced matchings on method invocations. These classes can be used to set up more complex expectations.

By following these guidelines, you can effectively use test doubles in PHPUnit to improve your testing workflow and ensure the correctness of your code.