单元测试 - AssertionFailedError - Java

Question

I'm having troubles understanding why this unit test is not working. I'm creating two instances of @RegionWithActivities and I thought that it should pass the test.

    @Test
    void testAreEqual()
    {
        RegionWithActivities regionWithActivities1 = new RegionWithActivities(4, regions);
        RegionWithActivities regionWithActivities2 = new RegionWithActivities(4, regions);

        assertEquals(regionWithActivities1, regionWithActivities2);
    }

The error is:

org.opentest4j.AssertionFailedError: expected: com.luciaandres.analysis.RegionWithActivities@710726a3<RegionWithActivities{numberOfActivities=4, regionIds=[4DA19B2B1328127FC062FB79F6F435A5, B66FA66DA650717E0964A4E30A716DAE, C841C0BED1CCDD643955065A696EED34, F2D04F76EA1EBD6C8E3AEDD506FBA35A]}> but was: com.luciaandres.analysis.RegionWithActivities@646007f4<RegionWithActivities{numberOfActivities=4, regionIds=[4DA19B2B1328127FC062FB79F6F435A5, B66FA66DA650717E0964A4E30A716DAE, C841C0BED1CCDD643955065A696EED34, F2D04F76EA1EBD6C8E3AEDD506FBA35A]}>
Expected :RegionWithActivities{numberOfActivities=4, regionIds=[4DA19B2B1328127FC062FB79F6F435A5, B66FA66DA650717E0964A4E30A716DAE, C841C0BED1CCDD643955065A696EED34, F2D04F76EA1EBD6C8E3AEDD506FBA35A]}
Actual   :RegionWithActivities{numberOfActivities=4, regionIds=[4DA19B2B1328127FC062FB79F6F435A5, B66FA66DA650717E0964A4E30A716DAE, C841C0BED1CCDD643955065A696EED34, F2D04F76EA1EBD6C8E3AEDD506FBA35A]}


    at RegionWithActivitiesTest.testAreEqual(RegionWithActivitiesTest.java:29)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)

Could you please explain me? Thanks!

Answer 1

When you use assertEquals ,it tries to compare two objects using equals() method.If you have not overriden equals() method from Object class in your class,the it uses the default equals() method from Object class which has implementation as below :

public boolean equals(Object obj) {
       return (this == obj);    
}

As you can see, here it just compares object reference and because two objects have two different references in your case, the assertion is failing, so you need to implement equals() method in RegionWithActivities class and as a best practice when you override equals(), you should override hashcode() method as well, but it is not necessary for your assertion to pass.

Answer 2

Theoretically, it's possible to just implement equals in RegionWithActivities to make your test case pass as assertEquals asserts based on equals() of RegionWithActivities . But implementing just equals() and not implementing hashcode() would violet Object class contract 2 as mentioned below -

The general contract of hashCode is:

1. Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
2. If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
3. It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.