How to avoid inheritance in JUnit test cases?

Question

I have a number of test cases in JUnit. All of them need the same code to be executed in their @BeforeClass static method. It's a code duplication and I'm trying to get rid of it. A dirty way of doing this is by inheritance. Are there any other mechanisms in JUnit, that may help?

PS. I wrote this blog post about this very subject: http://www.yegor256.com/2015/05/25/unit-test-scaffolding.html

Answer 1

The JUnit way to compose reusable code (instead of inheriting from it) are Rules.

See https://github.com/junit-team/junit/wiki/Rules

Here is a dumb sample, but you'll get the point.

import org.junit.rules.TestRule; import org.junit.runners.model.Statement; import org.junit.runner.Description;  public class MyTestRule implements TestRule {   @Override   public Statement apply(final Statement statement, Description description) {     return new Statement() {       public void evaluate() throws Throwable {         // Here is BEFORE_CODE         try {           statement.evaluate();         } finally {           // Here is AFTER_CODE         }       }     };   } } 

You can then use your TestRule like this:

import org.junit.Rule;  public class MyTest {     @Rule     public MyTestRule myRule = new MyTestRule(); } 

BEFORE_CODE and AFTER_CODE will then be executed around each of your test methods.

If you need to run your code only once per class, use your TestRule as a @ClassRule:

import org.junit.ClassRule;  public class MyTest {     @ClassRule     public static MyTestRule myRule = new MyTestRule(); } 

Now, BEFORE_CODE and AFTER_CODE will be executed around each of your test class.

@Rule field is not static, @ClassRule field is.

A @ClassRule can be declared in a Suite too.

Note that you can declare several rules in a single test class, that's how you compose test lifecycles at test-suites, test-classes and test-methods levels.

A Rule is an object that you instanciate in your test classes (statically or not). You can add contructor parameters if needed.

HTH

Answer 2

If the method is some kind of utility, then separate it out to a different class with a static method and call that method in your @BeforeClass.

I emphasize on the fact that don't use inheritance just because it solves your problem, use it when doing so creates sense in your class hierarchy.