Yes, it calls equals and there is a separate method, assertSame , that uses == . Just to clear things up, assertEquals works with any object since all objects declare equals . Yes it does.

How do assertEquals work?

assertEquals. Asserts that two objects are equal. If they are not, an AssertionError is thrown with the given message. If expected and actual are null , they are considered equal.

What is the difference between assertSame and assertEquals?

assertEquals uses equals() method (that you should override in your class to really compare its instances) to compare objects, while assertSame uses == operator to compare them. So the difference is exactly the same as between == (compare by value) and equals (compare identity).