cast closure map to object with a private constructor in groovy

Question

I am using groovy to create some mock classes for a test case. I am basically creating dummy objects where all the methods return null so that i can run my testcase.

I am using the following syntax:

MessageFactory.instance = ["getMessage": {a,b,c,d -> "dummy"}] as MessageFactory

So here i am trying to overwrite the singleton instance with my on fake factory object. The problem is that MessageFactory's constructor happens to be a private method. This gives me an illigal access exception when i run the code above. Is there a away i can create a proxy in groovy and overcome the private constructor issue?

Answer 1

If you have access to the MessageFactory, and are willing to modify it, then you use the standard dependency-injection solution, as detailed here: mock singleton ..Though it's not particularly Groovy.

Otherwise, the best workaround I've found is to override the method(s) on the singleton instance itself, like so:

@Singleton
class Test{
    def method(){"Unmocked method called"}
}


def test = Test.instance
test.metaClass.method = {-> null}

test.method() // Now returns null

Naturally, as a singleton, this instance doesn't change (at least in theory)... So, overriding methods in this manner is effectively global.

Edit: Or you can use GMock, which supports constructor mocking (among other things).