JUnit Mockito测试失败并显示equalTo

Question

I am trying to understand why adding in equalTo is making my test fail. I have recreated the problem with a simple class and test.

The first test passes and the second test fails.

Sample Class

public class Class {

Map<String, Boolean> data = new HashMap<>();

public Map<String, Boolean> getData(boolean access) {
    if (!access) 
        return null;
    return data;
}}

Test Class

public class ClassTest {

@InjectMocks
private Class testObj;

@Test
public void testGetDataNull() {
    assertThat(testObj.getData(false), is(nullValue()));
}

@Test
public void testGetDataNull2() {
    assertThat(testObj.getData(false), is(equalTo(nullValue())));
}}

The test that fails is showing this error message

Expected: is <null>
  but: was null

Q: What is the difference between these?

Any insight is much appreciated!

Answer 1

It is because nullValue() returns a org.hamcrest.core.isNull object. So it is not equal to null , it is an object. However that object contains a matches method which will only match null , which is why is works.

As an aside, the test should probably just read assertNull(testObj.getData(false))

Answer 2

Your question is actually about Hamcrest, not Mockito.

you're testing if the actual value, ie testObj.getData(false) , which is null , is equal to the value returned by nullValue() , which is an instance of the IsNull() matcher. An instance of IsNull is not equal to null , hence the failure.

I'd recommend avoiding Hamcrest, which in my opinion is harder to use correctly and less elegant than AssertJ .

With AssertJ, you would write

assertThat(testObj.getData(false)).isNull();

No static method to guess anymore, and valid autocompleted fluent assertions instead.