Using Mockito to mock a local variable of a method

Question

I have a class A that needs to the tested. The following is the definition of A:

public class A {
    public void methodOne(int arg         


        

Answer 1

The best way to deal with such a problem is to use an injected Clock service, used to get new instances of DateTime. That way, your test can inject a mock Clock, which returns a specific DateTime instead of the current time.

Note that the new Java 8 time API defines such a Clock class, specifically for that purpose.

Answer 2

You cannot mock a local variable. What you could do, however, is extract its creation to a protected method and spy it:

public class A {
  public void methodOne(int argument) {
    //some operations
    methodTwo(int argument);
    //some operations
  }

  private void methodTwo(int argument) {
    DateTime dateTime = createDateTime();
    //use dateTime to perform some operations
  }

  protected DateTime createDateTime() {
    return new DateTime();
  }
}

public class ATest {
  @Test
  public void testMethodOne() {
    DateTime dt = new DateTime (/* some known parameters... */);
    A a = Mockito.spy(new A());
    doReturn(dt).when(a).createDateTime();
    int arg = 0; // Or some meaningful value...
    a.methodOne(arg);
    // assert the result
}

Answer 3

Sorry for the late reply.

This might be too much of a hassle, but if you mock the object that can give you the local variable, you can return a mock of it. I'd rather not restructure the code to make testing easier, but its something to consider.

public class A {

    DateTimeFactory factory;

    private void method() {
        DateTime dateTime = factory.getDateTime();
        //use dateTime to perform some operations
    }
}

In your test you can do something like: when(factoryMock.getDateTime()).doReturn(dateTimeMock)

The factory mock would need to be injected into the class somehow.