Programming Groovy 2

18.7 Mocking Using ExpandoMetaClass

We can intercept method calls in Groovy in another way, using the ​ExpandoMetaClass​ (see Section 13.2, ​Injecting Methods Using ExpandoMetaClass​, and Section 13.3, ​Injecting Methods into Specific Instances​). We don’t have to create a separate class as in the two approaches we’ve seen so far. Instead, we can create a closure for each method we want to mock, and set that into ​MetaClass​ for the instance being tested. Let’s look at an example.

Create a separate instance of ​ExpandoMetaClass​ for the instance being tested. This ​MetaClass​ will carry the mock implementation of collaborator methods.

In this example, shown in the following code, we create a closure for mocking ​println​ and set that into ...