RSpec uses double to create a test double. However, there are two aliases for this method mock and stub. When do we use which alias? It depends on what role the test double is fulfilling.
If the test double is the focus of the test, then you will be setting a message expectation on the double, which takes the "mock" role.
If the test double is not the focus, and you are simply stubbing out methods on an object, then this takes the "stub" role. You can often eliminate the number of method stubs by ignoring method calls using #as_null_object.
