[groovy-user] metaclass: how to replace and restore a method?

[Aled Sage]

Hi,

I'm having trouble with replacing and then restoring a method using
metaClass, to override behaviour for a test. Any help much appreciated.

In one of my tests, I inject:
Foo.metaClass.myBusinessLogic = { /* record stuff here */ }

That works well for intercepting the (expensive) call and recording it.
But everything in the test suite then subsequently fails because the
method is now a no-op! I've been trying to restore the original method
in the tearDown.

---
My attempts have involved code like that below. But for each of my
attempts, it keeps writing out "replacement".

class ReplacingAndRestoringMetaMethod {
public static void main(String[] args) {
def origMethod = Foo.metaClass.myBusinessLogic
//def origMethod2 =
Foo.metaClass.getMetaMethod("myBusinessLogic", new Object[0])

Foo.metaClass.myBusinessLogic = { println "replacement" }
Foo.metaClass.myBusinessLogic = origMethod

new Foo().myBusinessLogic()
}
}

public class Foo {
public void myBusinessLogic() { println "orig" }
}

Thanks, Aled

p.s. I'd prefer to use
http://docs.codehaus.org/display/GROOVY/Groovy+Mocks, but the code
hasn't been written to support such injection...

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[Paulo Gabriel Poiati]

One way to do this is using categories:

class Foo {

    def bar() {

        'Original'

    }

    

}

class FooTestCategory {

    

    static String bar(Foo foo) {

        'Mocked'

    }

    

}

def foo = new Foo()

assert "Original" == foo.bar()

use (FooTestCategory) {

    assert "Mocked"== foo.bar()

}

assert "Original" == foo.bar()

[]'s
Paulo Poiati

blog.paulopoiati.com

[Aled Sage]

Thanks Paulo, that works great.

It was made a bit more complicated by my app-under-test being multi-threaded, so I had to inject a thread factory that wraps each Runnable.run in a `use (FooTestCategory)`. Luckily I could inject that thread factory using another test category :-)

Thanks again for the fast response,

Aled

[Dinko Srkoc]

On 2 December 2011 19:29, Aled Sage <aled...@cloudsoftcorp.com> wrote:
> Hi,
>
> I'm having trouble with replacing and then restoring a method using
> metaClass, to override behaviour for a test. Any help much appreciated.
>
> In one of my tests, I inject:
>        Foo.metaClass.myBusinessLogic = { /* record stuff here */ }
>
> That works well for intercepting the (expensive) call and recording it. But
> everything in the test suite then subsequently fails because the method is
> now a no-op! I've been trying to restore the original method in the
> tearDown.
>

In order to restore the original method you might try putting this in
the tearDown:

GroovySystem.metaClassRegistry.removeMetaClass Foo

This may have the same effect:

Foo.metaClass = null

Cheers,
Dinko

[Coderextreme]

It looks like you have to have an instance before using categories. What do
you do if you don't have an instance, for example, I am replacing the method
static method bar in class Foo:

Foo.metaClass.'static'.bar = { "Mocked" }

What's the best way restore bar to it's original state? Or is there a
better solution (I hope).

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[Coderextreme]

This seems to work. I am not sure I like it though. Any better solutions?

class Foo {

static def bar() {
'Original'
}
}

assert "Original" == Foo.bar()

Foo.metaClass.'static'.bar = {"Mocked" }

assert "Mocked" == Foo.bar()

Foo.metaClass = null

assert "Original" == Foo.bar()

Foo.metaClass.'static'.bar = {"Mocked" }

assert "Mocked" == Foo.bar()

Foo.metaClass = null

assert "Original" == Foo.bar()

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[Edward Sumerfield]

Yes, that has worked for me too but if you have two methods, how would you revert just one to it's original version.

Ed

[Coderextreme]

http://stackoverflow.com/questions/8349077/how-do-i-reset-a-mocked-static-method-in-groovy

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