This test wont' fail if `assertError()` throws nothing. One common idiom for testing assertion messages is this:

    @Test
    public void arraysExpectedContainsNull() {
      try {
        assertArrayEquals(new Object[]{null}, new Object[]{true});
      } catch (AssertionError exception) {
        assertEquals("arrays first differed at element [0]; expected:<null> but was:<true>"
            exception.getMessage());
        return;
      }
      fail("Expected AssertionError to be thrown");
    }