Java 8: unit-testing a method that returns a Function object

Question

I'm trying to write a Java 8 unit test for a method that returns a Function; something like:

class MyObject<X> {
     public Function<X,Obj> getFunction() {...}
 }

In my unit test I create a sample Object and call getFunction() and want to compare that to the expected function which does not work with org.junit.Assert.assertEquals:

@Test
public void getFunction_returnsFunction() {
   final MyObject<St> object = new MyObject<>(..);
   final Function<St,Obj> expectedResult = ...;

   // this does not work
   assertEquals(expectedResult, object.getFunction());
}

Is it even possible to compare two Functions? How would you recommend to unit test this method?

Answer 1

Check the function behavior using the standard R Function.apply(T t) method:

Function<St,Obj> func = o.getFunction();
assertEquals(func.apply(value), expectedFunctionResult);