The Spock testing framework currently does not support partial mocks. It is easy to mock out a class, but not individual methods in a class.

In almost all cases, this makes sense to me. If you really only want to mock out only one method, maybe you need to refactor the code to create a new class. While this is good in theory, it is not always practically possible.

In these cases, you could use Groovy’s meta-programming to accomplish partial mocks.

Let’s say you have a simple class like this:

class MyClass {
    def doSomethingCool(){
        if(findBooleanValue()){
            return 1
        } else {
            return 2
        }
    }

    def findBooleanValue() {
        //do something complicated to determine value
        return true
    }
}

If I just wanted to mock out the findBooleanValue method, but test the actual functionality of the doSomethingCool() method, I could write a spock test like this:

def 'test with partial mocks' () {
    given: 'an instance of the class to test'
    def testClass = new MyClass()

    and: 'partial mock findBooleanValue method'
    testClass.metaClass.findBooleanValue = {false}

    expect: 'the method should be overridden'
    testClass.doSomethingCool() == 2
}

Here I used simply used Groovy’s metaClass to change how the findBooleanValue method acts.