Testing arguments of method execution with Spock Framework

Testing arguments of method execution with Spock Framework

Testing value returned from a method is easy. Each basic tutorial of unit testing covers that. Checking if a specific method has been executed at all is not that simple but possible. In this post, I show how to check if a particular method was executed with a certain argument. All of this is presented in Spock Framework.

 I have a method to test:

public Long addAppleToBasket(Long basketId, double weight) throws EmployeeNotFoundException {
    Basket basket = basketsRepository.findOne(basketId);
    if (basket == null) {
        throw new BasketNotFoundException();
    }

    Apple apple = new Apple(weight);

    basketsRepository.save(apple);
    return apple.getId();
}

Honestly, in real life it is not a good candidate to test as there is not much of business logic, but that is not the point of this article. It is just an example.

I am not interested in testing the returned value - an ID as it is a sequential number with no business value. But the most important is what was saved in the repository.

A unit test in Spock Framework looks like this:

def "test addAppleToBasket"() {
    given:
    Basket basket = Mock()
    basketsRepository.findOne(3) >> basket

    when:
    basketService.addAppleToBasket(3, 0.123)
    then:
    1 * basketsRepository.save(_) >> { arguments ->
        final Apple apple = arguments.get(0)
        assert apple == new Apple(weight: 0.123)    }
}

1 * method means that the method is expected to be executed with any argument (_) exactly once during the test. The second part tells Spock that the first argument of the method should be an object of the Apple class. The assertion line is a concise way to instruct Spock to check what the argument really should be. In this case, it should be an apple with weight = 0.123.