Java – JUnit confusion: use ‘extends TestCase’ or ‘@Test’

automated-testsjavajunit

I've found the proper use (or at least the documentation) of JUnit very confusing.
This question serves both as a future reference and as a real question.

If I've understood correctly, there are two main approaches to create and run a JUnit test:

Approach A (JUnit 3-style): create a class that extends TestCase, and start test methods with the word test. When running the class as a JUnit Test (in Eclipse), all methods starting with the word test are automatically run.

import junit.framework.TestCase;

public class DummyTestA extends TestCase {

    public void testSum() {
        int a = 5;
        int b = 10;
        int result = a + b;
        assertEquals(15, result);
    }
}

Approach B (JUnit 4-style): create a 'normal' class and prepend a @Test annotation to the method. Note that you do NOT have to start the method with the word test.

import org.junit.*;
import static org.junit.Assert.*;

public class DummyTestB {

    @Test
    public void Sum() {
        int a = 5;
        int b = 10;
        int result = a + b;
        assertEquals(15, result);
    }
}

Mixing the two seems not to be a good idea, see e.g. this stackoverflow question:

Now, my questions(s):

  1. What is the preferred approach, or when would you use one instead of the other?
  2. Approach B allows for testing for exceptions by extending the @Test annotation like in @Test(expected = ArithmeticException.class). But how do you test for exceptions when using approach A?
  3. When using approach A, you can group a number of test classes in a test suite like this:

    TestSuite suite = new TestSuite("All tests");
    suite.addTestSuite(DummyTestA.class);
    suite.addTestSuite(DummyTestAbis.class);

    But this can't be used with approach B (since each testclass should subclass TestCase). What is the proper way to group tests for approach B?

Edit: I've added the JUnit versions to both approaches

Best Solution

The distinction is rather easy:

  • extending TestCase is the way unit tests were written in JUnit 3 (of course it's still supported in JUnit 4)
  • using the @Test annotation is the way introduced by JUnit 4

Generally you should choose the annotation path, unless compatibility with JUnit 3 (and/or a Java version earlier than Java 5) is needed. The new way has several advantages:

To test for expected exceptions in a JUnit 3 TestCase you'd have to make the text explicit.

public void testMyException() {
  try {
    objectUnderTest.myMethod(EVIL_ARGUMENT);
    fail("myMethod did not throw an Exception!");
  } catch (MyException e) {
    // ok!
    // check for properties of exception here, if desired
  }
}

JUnit 5 introduced yet another API change, but still uses annotations. The new @Test annotation is org.junit.jupiter.api.Test (the "old" JUnit 4 one was org.junit.Test), but it works pretty much the same as the JUnit 4 one.