Golang: Which directory to put mocks?

I've been most recently experimenting with GoMock, the test mocking framework supported by the official creators of the Go language. I was wondering where is the most reasonable place to put these mocked files.

My current directory structure is as follows. Is this how Go projects should be structured?

appname
|-- gateways
    |-- gateway1.go
    |-- gateway1_test.go
    |-- gateway2.go
    |-- gateway2_test.go
    |-- mocks
        |-- gateway1.go
        |-- gateway2.go

This is slightly influenced by Ben Johnson's talk here.