Mocking and stubbing in Groovy with ‘with’

I often use metaClass in Groovy to create mocks or stubs in my unit tests. Recently I’ve discovered that the with method makes this a bit simpler.

This:

Foo.metaClass.with {
  doSomething = {
    return true
  }
  anotherThing = {foo ->
    assertEquals 42, foo
  }
}

is slightly shorter than this:

Foo.metaClass.doSomething = {
  return true
}
Foo.metaClass.anotherThing = {foo ->
  assertEquals 42, foo
}

and less code means less bugs.

[Update: For more explanation of why the with method is so great, read this post.]
[Update: And for another way to write your mocks and stubs, see my previous post on mocking with Groovy.]