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| author | version | line-number | content |
|---|---|---|---|
| 1 | === Purpose === | ||
| 2 | |||
| 3 | * Mocking simplifies unit testing by replacing the dependencies of the unit being tested with simplified, simulated versions called mocks. | ||
| 4 | * Example: Consider a unit under test that relies on a database. In testing, the database can be mocked to return a static value, eliminating the need for an actual database. | ||
| 5 | |||
| 6 | === Benefits of Mocking === | ||
| 7 | |||
| 8 | * Isolation of units to test each unit separately, dramatically reducing complexity and increasing test execution speed by replacing loaded modules with mocks. | ||
| 9 | * Simplifies the re-creation of specific scenarios (use cases, boundary cases). | ||
| 10 | * Expose hidden internals of production code without compromising encapsulation. | ||
| 11 | * Injection of test-specific behaviors not present in production code. | ||
| 12 | * Enables the simulation of indirect dependencies by letting mocks return other mocks. | ||
| 13 | |||
| 14 | === Types of Mocks === | ||
| 15 | |||
| 16 | (% style="text-align: justify;" %) | ||
| 17 | Stubs are by far the most common type of mock. Keep your tests as simple as possible. Make them more complex only when necessary. | ||
| 18 | |||
| 19 | * **Stubs**: Simplest form, returning a hardcoded value or providing an empty method body. | ||
| 20 | * **Fake object**: Include minimal logic to handle different case scenarios. | ||
| 21 | * **Spy**: Injected to capture interaction data with fake objects when such data is not directly accessible. | ||
| 22 | * **Mock objects**: Contain complex logic, simulate behaviors such as computation and exception handling, and even run tests. | ||
| 23 | |||
| 24 | === Tips === | ||
| 25 | |||
| 26 | * **Mock third-party libraries for unit tests** to ensure proper unit functionality. Instead, use these libraries in component and integration tests. | ||
| 27 | * Aim for a **minimal number of dependencies in a unit** for easier testing and mocking: | ||
| 28 | ** Limit dependencies in a unit in a similar way to the best practices for function arguments: the fewer the better, with an absolute maximum of three. | ||
| 29 | ** Prefer many small classes/units to one large one for easier testing. | ||
| 30 | ** If a class has excessive dependencies, consider splitting it up or extracting some dependencies into a new class to create smaller, more cohesive units. | ||
| 31 | ** If a production class requires more than one test class, it's probably a sign that the class is too large. | ||
| 32 | ** Overly complex test code may indicate an overly large production class. |