JUnit test cases for custom method

I'm studying for my first job interviews as Junior Java Developer and right now I'm trying to learn JUnit test cases. This is an example that I encountered and I must say it's really tricky for me (it's abstract code so I have no idea how to test it).

public class JuiceMaker {

  public Juice makeJuice(final List<Fruit> fruits) throws RottenFruitException {
    for (final Fruit fruit : fruits) {
      if (FruitInspector.isFruitRotten(fruit)) {
        throw new RottenFruitException(fruit.getName() + “ is rotten. Cannot make juice.”);
      }
    }

    return Juicer.juice(fruits);
  }
} 

The only example I managed to create myself is this one:

JuiceMaker jm = new JuiceMaker();

@Test
public void isThrowingException() {
//when
  try {
      jm.throwsRuntime();
      Assert.fail("Expected exception to be thrown");
  } catch (RottenFruitException e) {
//then
      assertThat(e)
          .isInstanceOf(RottenFruitException.class)
          .hasMessage((fruit.getName() + " is rotten. Cannot make juice.");
  }
}

Any tips of what kind of tests I can perform on this piece of code? Thanks a lot for your help!