| Type | What it tests | Why | Who |
|---|---|---|---|
| Unit test | Functionality of one unit in isolation | Verify that the unit behaves as expected | Developer (preferably of the unit) |
| Integration test | Functionality, performance, or other quality characteristic of at least 2 classes | Verify that parts of the system work together | Developer |
| End-to-end test | System interaction (with a unit or other system) | Verify that the system behaves as expected | Developer |
| Regression test | Previously erroneous behavior of a unit, class, or system interaction | Ensure that bugs do not reappear | Developer |
| Acceptance test | System interaction (with a user or another system) | Confirm the system behaves as required | End-user representative (never the developer) |
It is crucial for all developers to learn how to write unit tests well.
- Test both normal and special cases
- Test the happy flow. Write tests that cover that the unit behaves like you want it to.
- Test the sad/rainy day flow. Write tests that confirm a unit behaves sensibly on non-normal or faulty input.
- Maintain tests just like nontest (production) code
- If you change a unit, also change the tests, and vice versa.
- Write isolated tests
- Never write tests depending on the state or other files written by other tests. If you need data then stub or mock it.
The approach of writing a unit test before writing the code that conforms to the test. Then writing the minimum amount of code to make the test pass.
Designing a method becomes easier if you think about how you are going to test it. What are the valid inputs/parameters, and what should the method return as a result?
- Automate tests
- Use test-driven development (TDD)