Published July 16, 2023
by Doug Klugh

Keep Tests Well Organized

Organize your xUnit test packages, classes, and methods in a way that makes it easy to find, understand, and maintain your tests.  While this is relatively easy with a small number of tests, effectively managing a lot of them takes some planning.  Although there is no single best practice, there are organizational strategies that will go a long way to help keep your tests and test fixtures well organized.  These strategies will also help to promote test code reuse, simplify running test subsets, manage the lifetime of test fixtures, and optimize test execution by managing resources that are expensive to allocate.

Test Class Strategies

How you organize your test methods will have a big impact on the efficiency of your testing.

Test Class per Class

The simplest approach to test organization is to simply create a test class for each production class.  This test class will contain all the test methods used to verify the behavior of a particular SUT class.  While this makes it easy to locate all the tests associated with that class, it may require creating a significant number of test fixtures.

Test Class per Feature

Another approach is to put all test methods that verify a particular feature or capability of the SUT into a single test class.  Not only does this make it easy to locate all the tests associated with a feature, but it is also easy to run that subset of tests that verify (and possibly validate) specific functionality.  The downside is that it may result in duplicate test fixtures (across different features).

Test Class per Fixture

One more approach is to group all test methods that require the same test fixture(s) into the same test class.  This will minimize the number of test fixtures but your tests for each feature will likely be scattered across numerous test classes — which may inhibit your ability to locate specific tests or to run a certain subset of tests.

Test Fixture Strategies

A Test Fixture is code that defines the context (pre-conditions) that is needed to exercise (and test) the SUT.  This, of course, would include an instance of the class whose method we are testing.  It may also include other objects upon which the SUT depends.  While we certainly would not create SUT dependencies for unit tests, they may likely be needed for other types of tests, such as component, acceptance, and integration tests. 

Following are a few strategies for optimizing test fixtures:

Transient Fresh Fixture

A Transient Fresh Fixture is one that is created and destroyed within every test.  This type of fixture is particularly easy to setup in JUnit using either a constructor or setup method (using the @Before attribute).  JUnit will invoke either one (or both) before each test method.  This type of fixture is transient because the lifetime of the fixture persists only for the duration of the test method.  And it is fresh because the fixture is initialized prior to each method. 

Transient Fresh Fixtures ensure that your tests are independent, can execute concurrently, and can execute in any order.  They also ensure that you never need a tear-down method because nothing persists beyond the fixture — it's all destroyed at the end of the test.  If you need a tear-down method, that's an indicator that there is something about the fixture that is not transient.

Persistent Fresh Fixture

A Persistent Fresh Fixture is one that otherwise persists from test to test and needs to be torn down within each test method to make it fresh.  Examples include fixtures that create resources such as files, sockets, semaphores, database connections, etc.  The goal of the tear-down method is to delete or reset any persistent parts of the fixture — making them fresh again for the next test.

Users of NUnit or x-Unit should note that these frameworks do not create a fresh instance between test methods — which means that all tests written in those frameworks are persistent.  This will require tear-down methods to freshen them up.

Persistent Shared Fixture

A Persistent Shared Fixture is one that allows some state (or resource) to persist from test to test.  Since some resources can be very expensive to create and destroy within every test method (such as database connections), it is usually best to share that resource across a suite of tests.  In JUnit, this can be accomplished using the @BeforeClass attribute to designate suite setups and the @AfterClass attribute to designate suite teardowns. 

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