How to Define JUnit Tests

Creating a JUnit (.java) Test File

• File → New → JUnit Test Case → New JUnit 4 test
• If the JUnit library is not part of the project you will get a message indicating whether it should be added; just add it.
• Pick a class name (e.g., MyClass or any name you prefer).

Writing JUnit Tests

• To create tests define public void methods that have the @Test annotation. For example:

@Test
public void checkingEvenValues() {
    ...
}

• Inside of a test method you can have typical Java code where assertions are used to specify the expected results for the test.
• The following are common assertions we use in JUnit tests:
  • assertTrue → verifies that the argument expression is true. If the argument expression is false the test fails; otherwise execution is successful.
  • assertEquals → takes two arguments (expected value and actual value). If the values are not equal the test fails; otherwise execution is successful.
  • assertFalse → verifies that the argument expression is false. If the argument expression is true the test fails; otherwise execution is successful.
• You can define auxiliary methods (e.g. private methods) that support the set of tests you are developing.
• You can have multiple assertions in a JUnit test. Once the first one fails the whole test is considered to had failed.
• Pick descriptive names for your test methods.


  Notes:
• If you don't provide an assertion a test is not considered to fail.
• The use of static fields can lead to results from one test to propagage to the next. See Example 2 (JUnitExample.zip) below.
• You can use the Eclipse debugger with JUnit tests.
• You can add output statements to see results generated by your tests.

• Example 1:

  public class AuxMath {
      public static int maximum(int x, int y) {
          if (x > y)
              return x;
          return y;
      }
  
      public static int minimum(int x, int y) {
          if (x < y)
              return x;
          return y;
      }
  }
  
  import static org.junit.Assert.*;
  import org.junit.Test;
  
  public class JUnitTestExample {
      @Test
      public void oneMaximum() {
          int expectedResults = 20;
          assertEquals(expectedResults,  AuxMath.maximum(10, 20));
      }
  
      @Test
      public void twoMinimum() {
          int expectedResults = 5;
          assertTrue(expectedResults==AuxMath.minimum(30, 5));
      }
  }
  

• Example 2: JUnitExample.zip

• In JUnit4 you can run tests based on their name by using the annotation @FixMethodOrder(MethodSorters.NAME_ASCENDING) before the class name. For example:

  @FixMethodOrder(MethodSorters.NAME_ASCENDING)
  public class JUnitTestExample {
  

  Make sure you add the following imports to the file:

  import org.junit.FixMethodOrder;
  import org.junit.runners.MethodSorters;
  

• Reference: Additional information can be found at JUnit Tutorial by Lars Vogel.