### Question:
ClassAndFieldKey implements Comparable<ClassAndFieldKey> { @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final ClassAndFieldKey other = (ClassAndFieldKey) obj; if (this.className != other.className && (this.className == null || !this.className.equals(other.className))) { return false; } if (this.fieldName != other.fieldName && (this.fieldName == null || !this.fieldName.equals(other.fieldName))) { return false; } return true; } ClassAndFieldKey(String className, String fieldName); String getClassName(); String getFieldName(); @Override String toString(); @Override int hashCode(); @Override boolean equals(Object obj); @Override int compareTo(ClassAndFieldKey o);  }### Answer:
@Test(dataProviderClass = ClassAndFieldTestDataProvider.class, dataProvider = "createClassFieldPair") public void testEquals(String className1, String fieldName1, String className2, String fieldName2, boolean expectedEqual, int expectedCompare) { ClassAndFieldKey key1 = new ClassAndFieldKey(className1, fieldName1); ClassAndFieldKey key2 = new ClassAndFieldKey(className2, fieldName2); Assert.assertEquals(expectedEqual, key1.equals(key2), "are equal meet the expectation?"); if (expectedEqual) { Assert.assertEquals(0, key1.compareTo(key2), "equal means compare == 0"); Assert.assertEquals(key1.hashCode(), key2.hashCode(), "equals means same hashcode"); } if (expectedCompare < 0) { Assert.assertTrue(key1.compareTo(key2) < 0, "are compare <0?" + key1.compareTo(key2)); } else if (expectedCompare > 0) { Assert.assertTrue(key1.compareTo(key2) > 0, "are compare > 0?"); } else { Assert.assertTrue(key1.compareTo(key2) == 0, "are compare ==0 ?"); } Assert.assertEquals(key1 == null, false, "null object is not equal to any object"); Assert.assertEquals(key1.equals(key1), true, "object is equal to self object"); Assert.assertEquals(key1.equals(new ObjectId("myclass", new Id(2))), false, "other type of object is not equal to this kind of object"); }