What are the most common Java testing anti-patterns and how can you avoid them?

1 Hard-coded values

One of the most common testing anti-patterns is using hard-coded values in your tests. Hard-coded values are literals or constants that are directly written in your test code, such as numbers, strings, or dates. They make your tests brittle, because they can break if the application logic or data changes. They also make your tests unclear, because they do not explain what they represent or why they are important. To avoid hard-coded values, you should use meaningful names and variables for your test data, and extract them into reusable methods or classes. You should also use data-driven testing frameworks, such as JUnitParams or TestNG, that allow you to parameterize your tests with different inputs and outputs.

2 Test interdependence

Another common testing anti-pattern is creating tests that depend on each other. Test interdependence means that the outcome of one test affects the outcome of another test, either directly or indirectly. This can happen when you share state between tests, such as static fields, global variables, or database records. It can also happen when you rely on the execution order of tests, such as expecting a test to run before or after another test. Test interdependence makes your tests unpredictable, because they can fail or pass for the wrong reasons. It also makes your tests hard to maintain, because you have to update multiple tests if you change one test. To avoid test interdependence, you should make your tests isolated and independent. You should use the @Before and @After annotations to set up and tear down the test environment for each test. You should also use the @Test annotation to specify the expected behavior and outcome of each test, without assuming anything about other tests.

3 Magic numbers

A related testing anti-pattern is using magic numbers in your tests. Magic numbers are numeric values that appear in your test code without any explanation or context. They can be hard-coded values, such as 42 or 3.14, or they can be derived from calculations or formulas, such as 2 * 5 + 1. They make your tests obscure, because they do not convey the meaning or purpose of the numbers. They also make your tests fragile, because they can change if the application logic or requirements change. To avoid magic numbers, you should use descriptive names and constants for your numeric values, and explain how they are calculated or obtained. You should also use assert methods that compare the actual and expected values, and provide a message that explains the reason for the assertion.

4 Test duplication

Another testing anti-pattern is duplicating test code across multiple tests. Test duplication means that you have the same or similar code in different test methods or classes, such as setting up the test data, invoking the system under test, or verifying the results. It can happen when you copy and paste test code, or when you do not refactor your test code to eliminate redundancy. Test duplication makes your tests verbose, because they have a lot of unnecessary or repeated code. It also makes your tests difficult to change, because you have to modify multiple tests if you change one test. To avoid test duplication, you should follow the DRY (Don't Repeat Yourself) principle, and extract the common code into reusable methods or classes. You should also use the @BeforeClass and @AfterClass annotations to perform common actions before and after all tests in a class. You should also use inheritance or composition to share test code between different test classes.

5 Test sprawl

A final testing anti-pattern is having too many tests that cover the same or trivial functionality. Test sprawl means that you have more tests than you need, or that your tests are too long or complex. It can happen when you write tests without a clear strategy or focus, or when you do not prioritize or categorize your tests. Test sprawl makes your tests slow, because they take a long time to run and consume a lot of resources. It also makes your tests noisy, because they produce a lot of output or errors that are not relevant or important. To avoid test sprawl, you should follow the FIRST (Fast, Independent, Repeatable, Self-Verifying, Timely) principle, and write tests that are concise, focused, and meaningful. You should also use the @Ignore annotation to skip tests that are not ready or relevant. You should also use test suites or categories to group and organize your tests according to different criteria, such as functionality, priority, or environment.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?