Groovy's 'as' operator can be used with closures in a neat way which is great for developer testing in simple scenarios. We haven't found this technique to be so powerful that we want to do away with dynamic mocking, but it can be very useful in simple cases none-the-less.
Suppose we are using Interface Oriented Design and as sometimes advocated we have defined a number of short interfaces as per below. (Note: we ignore the discussion about whether interfaces are as valuable a design approach when using dynamic languages that support duck-typing.)
To testing this, we could use Groovy's built-in mocking or some other dynamic mocking framework. Alternatively, we could write our own static mocks. But no one does that these days I hear you say! Well, they never had the ease of using closures, which bring dynamic power to static mocks, so here we go:
That was easy.