Testing Private method using mockito

Question

public class A {

    public void method(boolean b){
          if (b == true)
               method1();
          else
               method2();
    }

    private void method1() {}
    private void method2() {}
}

public class TestA {

    @Test
    public void testMethod() {
      A a = mock(A.class);
      a.method(true);
      //how to test like    verify(a).method1();
    }
}

How to test private method is called or not, and how to test private method using mockito???

Answer 1

You're not suppose to test private methods. Only non-private methods needs to be tested as these should call the private methods anyway. If you "want" to test private methods, it may indicate that you need to rethink your design:

Am I using proper dependency injection? Do I possibly needs to move the private methods into a separate class and rather test that? Must these methods be private? ...can't they be default or protected rather?

In the above instance, the two methods that are called "randomly" may actually need to be placed in a class of their own, tested and then injected into the class above.

Answer 2

Put your test in the same package, but a different source folder (src/main/java vs. src/test/java) and make those methods package-private. Imo testability is more important than privacy.

Answer 3

You can't do that with Mockito but you can use Powermock to extend Mockito and mock private methods. Powermock supports Mockito. Here's an example.

Answer 4

Here is a small example how to do it with powermock

public class Hello {
    private Hello obj;
    private Integer method1(Long id) {
        return id + 10;
    }
} 

To test method1 use code:

Hello testObj = new Hello();
Integer result = Whitebox.invokeMethod(testObj, "method1", new Long(10L));

To set private object obj use this:

Hello testObj = new Hello();
Hello newObject = new Hello();
Whitebox.setInternalState(testObj, "obj", newObject);

Answer 5

There is actually a way to test methods from a private member with Mockito. Let's say you have a class like this:

public class A {
    private SomeOtherClass someOtherClass;
    A() {
        someOtherClass = new SomeOtherClass();
    }
    public void method(boolean b){
        if (b == true)
            someOtherClass.method1();
        else
            someOtherClass.method2();
    }

}

public class SomeOtherClass {
    public void method1() {}
    public void method2() {}
}

If you want to test a.method will invoke a method from SomeOtherClass, you can write something like below.

@Test
public void testPrivateMemberMethodCalled() {
    A a = new A();
    SomeOtherClass someOtherClass = Mockito.spy(new SomeOtherClass());
    ReflectionTestUtils.setField( a, "someOtherClass", someOtherClass);
    a.method( true );

    Mockito.verify( someOtherClass, Mockito.times( 1 ) ).method1();
}

ReflectionTestUtils.setField(); will stub the private member with something you can spy on.