Stub a void method in a Spy object with Spock

Question

I'm using Spock and my class to test is wrapped in a Spy. I want to isolate the method being tested, so I'm trying to stub out other methods that are called from the method being tested. Normally I would use something like this:

1 * classToTest.methodName(_) >> stubbed_return_value

My problem is this: methodName is a void method. I tried this:

1 * classToTest.methodName(_)

but the actual method is still called.

How do I stub out a void method using Spock?

Answer 1

You can just stub it with null...

Given the following Java class:

public class Complex {
    private final List<String> sideEffects = new ArrayList<>();

    protected void sideEffect(String name) {
        sideEffects.add("Side effect for " + name);
    }

    public int call(String name) {
        sideEffect(name);
        return name.length();
    }

    public List<String> getSideEffects() {
        return sideEffects;
    }
}

We want to hide the sideEffect method, so nothing is done by it, so we can use the following spec:

class ComplexSpec extends Specification {
    def 'we can ignore void methods in Spies'() {
        given:
        Complex complex = Spy()

        when:
        int result = complex.call('tim')

        then:
        result == 3
        1 * complex.sideEffect(_) >> null
        complex.sideEffects == []
    }
}

Answer 2

You could also return an empty closure (instead of a null):

1 * complex.sideEffect(_) >> {}