AssertJ has many useful methods to write assertions using a fluid API. If we want to test the toString() method implementation of an object we can of course invoke the toString() method inside an assertThat expression and check with the assert method isEqualTo(String) the value. But AssertJ can make that easier so we don’t have to invoke toString() method ourselves. We can use the assert method hasToString(String) on the object we defined in the assertThat expression and specify our expected value as argument to the method. If we want to assert the toString() method doesn’t return an expected value we can use the assert method doesNotHaveToString(String).