How to write Junit test to test if the method has thrown an exception correctly?

Question

How to test if the following method has throw the exception when the name is null?

public boolean validateName(String name) {
    if (name == null) {
        throw new IllegalArgumentException("Name cannot be null");
    }
    if (name.isBlank()) { // checks if name is entirely whitespace
        return false;
    }
    if (!name.contains(" ")) {
        return false;
    }
    return true;
}

I have already test all the cases for blank name, and name containing spaces, the only one that have left is the test for when the name is null, here is what i have got:

@Test
public void handlesNullTest() {
    String name = null;
    NameValidator validator;
    assertEquals("Name cannot be null", validator.validateName(name));
    
}

Is above the correct way to test for throwing exception in java Junit test? thank you.

"*Is above the correct way to test for throwing exception in java Junit test?*" - No. — Turing85, Aug 29 '21 at 15:35

score 0 · Answer 1 · answered Aug 29 '21 at 15:36

0

With Junit 4 you can use as attribute for @Test annotation an attribute to "expect" a certain exception, like the following:

@Test(expected = IllegalArgumentException.class)
public void whenExceptionThrown_thenExpectationSatisfied() {
  String name = null;
  NameValidator validator;
  validator.validateName(name);
}

answered Aug 29 '21 at 15:36

Vokail

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JUnit4 is pretty outdated. We should use junit jupiter instead. – Turing85 Aug 29 '21 at 15:37

How to write Junit test to test if the method has thrown an exception correctly?

1 Answers1