Learn mocking with Gomock

Installation

We need to install the gomock package github.com/golang/mock/gomock as well as the mockgen code generation tool github.com/golang/mock/mockgen. Install both packages using go install go install github.com/golang/mock/gomock go install github.com/golang/mock/mockgen

If you have $GOPATH/bin in your $PATH, you can verify that the binary was installed successfully by running mockgen. If $GOPATH/bin is not in your $PATH you have to call mockgen via $GOPATH/bin/mockgen. In our example below we assume we have $GOPATH/bin in our $PATH.

Basic Usage

Usage of GoMock follows four basic steps:

Use mockgen to generate a mock for the interface you wish to mock.
In your test, create an instance of gomock.Controller and pass it to your mock object's constructor to obtain a mock object.
Call EXPECT() on your mocks to set up their expectations and return values.
Call Finish() on the mock controller to assert the mock's expectations.

Generating mocks

You can invoke the mockgen tool manually (e.g mockgen -destination=mocks/mock_doer.go -package=mocks github.com/basebandit/mocking/doer Doer) or use the go:generate (e.g. go generate ./...) tool to invoke it for you. mockgen takes the following arguments:

-destination=mocks/mock_doer.go:put the generated mocks in the file mocks/mock_doer.go
-package=mocks:put the generated mocks in the package mocks
github.com/basebandit/mocking/doer:generate mocks for this package.
Doer:generate mocks for this interface. This argument is required - we need to specify the interfaces to generate mocks for explicitly. We can however specify multiple interfaces here as a comma-separated list(e.g Doer1,Doer2).