assertThrows(IllegalArgumentException.class, () -> cms.removeExactly("a", -2));

    assertTrue(cms.removeExactly("a", 0));
    assertEquals(2, cms.count("a"));
    assertTrue(cms.removeExactly("c", 0));
    assertEquals(0, cms.count("c"));

    assertFalse(cms.removeExactly("a", 4));
    assertEquals(2, cms.count("a"));
    assertTrue(cms.removeExactly("a", 2));
    assertEquals(0, cms.count("a"));