Might be splitting hairs. There are fakes, mocks, and stubs. Generally, mocks assert, stubs do not. Some folks define both stubs and mocks as fakes. This does not fit perfectly for Go. The "fake" in Go is just a struct that matches an interface but is purely for testing. It allows for dependency injection where you pass a fake designed for your test. It can have its own properties and helper methods, but the key thing is that it matches your interface. You don't make assertions against the fake like you would a mock. You assert against responses from your functions under test.

Example:

  >  type Bar interface{
  >     Walk() (int, error)
  >  }
  >  
  >  func Visit(b Bar) (string, error) { ... some code ...}

In the production code, you call Visit with some struct that matches the interface (has a Walk method). In tests, you create a new struct like fakeBar that also matches the interface. You can have your fakeBar return any string or error you like and you can verify that Walk behaves the way you need it to.

Hope that helps.