Mocking ZonedDateTime Java8

Question

I have a model constructor that generates a timestamp as this.timestamp = null == timestamp? ZonedDateTime.now().toInstant().toEpochMilli(): timestamp; this.timestamp = null == timestamp? ZonedDateTime.now().toInstant().toEpochMilli(): timestamp;

How to mock ZonedDateTime? I need to validate using the test case that the value of the timestamp is the current time in milliseconds.

Since it is a model, injecting a dependency of a separate clock class is not possible in the constructor and I do not wish to change the source code.

Answer 1

It depends on your class and what you want to do:

1. If you want to mock all properties of a class, and the class is not final, then use a mocking framework like Mockito .

    MyClass mocked = Mockito.mock(MyClass.class); Mockito.when(mocked.getTimestamp()).thenReturn(**/ your value **/ )

2. If your class is final, you want to only mock this single property or then property is final:

You can create a static factory, that provides you with Instant and then in your test replace the factory.

 class TimeFactory {

  private static Supplier<Instant>  INSTANT_SUPPLIER = Instant::now;
  public static Instant getInstant(){ return INSTANT_SUPPLIER.get(); }
  public static void setInstantSupplier(Supplier<Instant> new){ INSTANT_SUPPLIER= supplier; } 
} 

And in your constructor:

this.timestamp = null == timestamp ? TimeFactory.getInstant().toEpochMilli() : timestamp;

Now in your test, you can us the setter method:

 TimeFactory.setInstantSupplier(()-> /*Your value*/ )
 // create your object

Just remember to return to default supplier after the test:

TimeFactory.setInstantSupplier(Instant::now);

3. If your property is not final, then add a package setter, that can be used in your test.

4. Next solution (not recommended though) is to use reflection . But this is not mocking, this is using force to set a private (event final) properties.

5. There is also a way to overwrite the clock for tests