Mock

mock is a code generation tool meant to be used with go generate. It generates simple mock implementations of interfaces for use in testing.

Mocks are thread-safe.

Installation

You can install mock locally using...

go install github.com/nathanjcochran/mock@latest

...or just use go:generate go run github.com/nathanjcochran/mock@latest to have the go generate command automatically use the latest version (see below for example usage).

Usage

The only required argument to mock is the name of the interface to mock, which must be provided after all other flags:

Usage: mock [options] interface
Options:
  -d string
    	Directory to search for interface in (default ".")
  -o string
    	Output file (default stdout)

Example

Given this interface:

package main

type Getter interface {
	GetByID(id int) ([]string, error)
	GetByName(name string) ([]string, error)
}

mock Getter will generate an implementation like this, and print it to stdout:

package main

// GetterMock is a mock implementation of the Getter
// interface.
type GetterMock struct {
	GetByIDStub     func(id int) ([]string, error)
	GetByIDCalled   int32
	GetByNameStub   func(name string) ([]string, error)
	GetByNameCalled int32
}

var _ Getter = &GetterMock{}

// GetByID is a stub for the Getter.GetByID
// method that records the number of times it has been called.
func (m *GetterMock) GetByID(id int) ([]string, error) {
	atomic.AddInt32(m.GetByIDCalled, 1)
	return m.GetByIDStub(id)
}

// GetByName is a stub for the Getter.GetByName
// method that records the number of times it has been called.
func (m *GetterMock) GetByName(name string) ([]string, error) {
	atomic.AddInt32(m.GetByNameCalled, 1)
	return m.GetByNameStub(name)
}

Go Generate

To use with go generate, simply place a go:generate comment somewhere in your package (e.g. above the interface definition), like so:

//go:generate go run github.com/nathanjcochran/mock@latest -o getter_mock.go Getter

Note the use of the -o flag, which specifies the output file. If this flag is not provided, the mocked implementation will be printed to stdout.

Then run the go generate command from the package directory.

Voila! There should now be a getter_mock.go file containing your new mock, in the same package as the interface definition. Subsequent runs of go generate will overwrite the file, so be careful not to edit it!