Question

Is it possible to Mock a single method of a Java class?

For example:

class A {
    long method1();
    String method2();
    int method3();
}


// in some other class
class B {
    void someMethod(A a) {
       // how would I mock A.method1(...) such that a.method1() returns a value of my
       // choosing;
       // whilst leaving a.method2() and a.method3() untouched.
    }
}

Answer 1

Use Mockito's spy mechanism:

A a = new A();
A aSpy = Mockito.spy(a);
Mockito.when(aSpy.method1()).thenReturn(5l);

The use of a spy calls the default behavior of the wrapped object for any method that is not stubbed.

Mockito.spy()/@Spy