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Always remember to tests all positive and negative scenarios and ensure that the proper results (error code, exception, message, etc.) are returned.
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Some error scenarios are extremely difficult to test using end-to-end or component tests, which makes testing all exception scenarios at the unit test level even more critical. |
Keep Related Tests Together
Try to keep tests that relate to a similar behavior together inside the test class. This makes it easier for other people to determine what's already been tested and what needs more testing.
Use Proper Assertions and Validations
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This best practice applies mostly to unit and component tests. Since End to End tests tend to be more complex and time consuming, it sometimes makes sense to verify related behavior in a single tests. This should however be avoided where if possible as doing so will make makes it more difficult to determine why a test failedwhat the issue is. |
Mock Dependencies
When writing unit or component tests, mock all dependencies that may fail. This allows the tests to guarantee that the unit or component under test behaves as excepted when one of its dependencies fails.
This is especially important in unit tests as these may be the only tests where some of those exception scenarios can be tested.
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Simply Simple dependencies (e.g., POJOs) or dependencies that are difficult to mock out (e.g., file system, static utility classes) can be used directly without being mocked, as long as doing so doesn't go against the basic testing best practices. |
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Use Existing Test Tools and Frameworks
Do not re-invent the wheel. Every homegrown mock, test tool or framework needs to itself be tested and maintained. There are tons of good testing frameworks and tools out there, use those instead.
Write Clean and Re-Usable Test Code
Maintain testing code as you would production code. This means keep the test code clean and extract re-usable code when it makes sense to do so.
Tests Before Changes
Before changing, fixing a bug or refactoring existing code, always make sure that tests exist and pass first.
If not, write unit test tests for the code that is about to be changed or refactored.
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Refactorings automatically performed by an IDE are usually safe and may not require adding tests first. This is especially true for simple structural refactorings that do not affect the logic or flow of the code, such as extract class, extract method, etc. If such refactorings make writing the tests easier, then applying them without existing tests can be considered. |
Be Test-Driven
Brendan Hofmann - I'm not sure I agree with this one. A lot of development is iterative in nature, and TDD can make that more expensive. We should have best-practices beyond TDD as well.
Steve Lombardi (Deactivated) - This seems OK but I wouldn't want developers to loose the flexibility to work how they work best.
Comment:
- Make it clear this is just a recommendation and doesn't always apply.
- Add "when appropriate" or "for new code" in title or description?
Follow Try tollow the Test-Driven Development Test CycleCycle when it makes sense and feel comfortable with it.
First, come up with an initial list of end to end, component and/or unit tests that will be needed to show that the user story, requirement or improvement works as expected or issue has been fixed.
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Test behaviors, not methods or lines of code.
Comment:
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This includes exceptional (e.g., error or unexpected) behaviors.
Write each test following the Behavior-Driven Development structure, i.e., Given/When/Then. In other words make sure each test:
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A test that requires many mocks usually indicates that the class under test is breaking the Single Responsibility Principle or the Law of Demeter and may need to be refactored.
Comments:
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Dependencies Difficult to Mock
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A Lot of Repeated Test Code
See Write Clean and Re-Usable Test Code
Creating Mocks Manually
See Use Existing Test Tools and Frameworks
Test Multiple Behaviors in a Single Test
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Repeated Given, When or Then sections in a BDD test, or difficult to name tests are usually two good indicators that a test is doing too much.
Comment:
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When testing behaviors that build on top of each other |
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(e.g., test step A, then test step B after step A has been done, etc.), consider extracting the common steps into private methods or external support class. This will reduce code duplication while ensuring that each test method verifies a specific behavior. |
Anti-Patterns
Sleeps
Sleeps in tests should be avoided as they open the door to timing issues and race conditions, slow tests down and are a major cause of test flakiness.
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Undoing Setups in Specific Tests
Common test fixtures that are run before all or each tests should remain common to all tests and should not be undone by individual tests. Doing so introduces a lot of confusion when reviewing, changing or maintaining the tests.
Instead, code that is common to many but not all tests should be extracted to one or more private methods or external support class to eliminate duplication.
Tests Need to be Run in a Specific Order
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