JUnit Test Failure

Question

I am trying to run a test on the class below:

package chapter03.backend;

import java.util.Map;

public class CharacterCounter {
    public static Map<Character, Integer> countCharacters(String text) {

         if (text == null) {
              throw new IllegalArgumentException("text must not be null");
            }
        return null;

    }
}

I have written this test class:

package chapter03.backend;

import static org.junit.Assert.*;

import org.junit.Test;

public class CharacterCounterTests {

    @Test(expected=IllegalAccessException.class)
    public void testNullInput() {
        CharacterCounter.countCharacters(null);
    }

}

When I run it, it keeps failing. Here is a screen shot of the error:

I will appreciate pointers on this.

Answer 1

IllegalAccessException is not IllegalArgumentException and is not a subclass of it either.

You throw indeed IllegalArgumentException in your tested method but you assert in the test that IllegalArgumentException is thrown.
Consequently, the assertion fails.

You should assert that IllegalArgumentException is expected:

@Test(expected=IllegalArgumentException.class)
public void testNullInput() {
    CharacterCounter.countCharacters(null);
}