Test Doubles Mocking (Symfony)

Use when

• A class under test depends on a collaborator that is slow, external or non-deterministic, such as a payment gateway or a message bus.
• An interaction must be verified, such as persist() and flush() or a dispatched message.
• A repository needs an in-memory fake implementing its interface.
• Choosing between a dummy, stub, mock, spy or fake.

Default workflow

1. Pick the double by need: stub to feed values, mock to verify a call, fake for a working simplified implementation.
2. Create it with $this->createMock(Interface::class) and stub with ->method('charge')->willReturn(...).
3. Verify only when the interaction matters: expects($this->once())->with(...), or $this->callback() to inspect a dispatched message.
4. Script behavior with willReturnOnConsecutiveCalls(), willThrowException() or willReturnCallback().
5. For repositories, write an InMemory fake implementing the interface.
6. Use ProphecyTrait with prophesize() and reveal() only if the project already relies on Prophecy.