Question

I’m learning JUnit, I know that assertEquals() invokes the equals() method to compare objects… so why the following test that compares two regex Pattern objects does not pass?

@Test
public void testTwoCompiledPattern()
{   
    assertEquals(Pattern.compile("test"), Pattern.compile("test"));
}

This one passes instead:

@Test
public void testTwoCompiledPattern()
{   
    assertEquals(Pattern.compile("test").toString(), Pattern.compile("test").toString());
}

Answer 1

Its because when you call the toString() method, both returns the “test” string because the Pattern class overrides it. But if you compare just the Pattern objects, they are 2 different objects, hence one is not equal to the other one, even though they have the same state.

The equals method checks for reference equality.