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Published: Apr 4, 2024 License: MIT Imports: 13 Imported by: 0


Interface mocking tool for go generate.

What is Moq?

Originally by (Mat Ryer and David Hernandez).

Moq is a tool that generates a struct from any interface. The struct can be used in test code as a mock of the interface.

Refer to example/ for basic usage.

This fork modernize the source code and improve some of its ergonomics. Hopefully, some of these changes will later be merged upstream.

This repository is covered by this SLA. If I decide to deprecate this package, I will maintain it for 3 months before archiving it.


You can use straight from the repository. Minimum required version is Go 1.22+.

moq [flags] source-dir interface [interface2 [interface3 [...]]]
  -fmt string
    	go pretty-printer: gofmt, goimports or noop (default gofmt)
  -out string
    	output file (default stdout)
  -pkg string
    	package name (default will infer)
    	first remove output file, if it exists
    	suppress mock implementation check, avoid import cycle if mocks generated outside of the tested package
    	return zero values when no mock implementation is provided, do not panic
    	show the version for moq
    	generate functions to facilitate resetting calls made to a mock

Specifying an alias for the mock is also supported with the format 'interface:alias'

Ex: moq -pkg different . MyInterface:MyMock

NOTE: source-dir is the directory where the source code (definition) of the target interface is located. It needs to be a path to a directory and not the import statement for a Go package.

In code (for go generate):

package my

//go:generate go run -out myinterface_moq_test.go . MyInterface

type MyInterface interface {
	Method1() error
	Method2(i int)

Then run go generate for your package.

How to use it

Mocking interfaces is a nice way to write unit tests where you can easily control the behavior of the mocked object.

Moq creates a struct that has a function field for each method, which you can declare in your test code.

In this example, Moq generated the EmailSenderMock type:

func TestCompleteSignup(t *testing.T) {

	var sentTo string

	mockedEmailSender = &EmailSenderMock{
		SendFunc: func(to, subject, body string) error {
			sentTo = to
			return nil

	CompleteSignUp("", mockedEmailSender)

	callsToSend := len(mockedEmailSender.SendCalls())
	if callsToSend != 1 {
		t.Errorf("Send was called %d times", callsToSend)
	if sentTo != "" {
		t.Errorf("unexpected recipient: %s", sentTo)


func CompleteSignUp(to string, sender EmailSender) {
	// TODO: this

The mocked structure implements the interface, where each method calls the associated function field.


  • Keep mocked logic inside the test that is using it
  • Only mock the fields you need
  • It will panic if a nil function gets called
  • Name arguments in the interface for a better experience
  • Use closured variables inside your test function to capture details about the calls to the methods
  • Use .MethodCalls() to track the calls
  • Use .ResetCalls() to reset calls within an individual mock's context
  • Use go:generate to invoke the moq command
  • If Moq fails with a go/format error, it indicates the generated code was not valid. You can run the same command with -fmt noop to print the generated source code without attempting to format it. This can aid in debugging the root cause.


The Moq project (and all code) is licensed under the MIT License.

Moq was created by Mat Ryer and David Hernandez, with ideas lovingly stolen from Ernesto Jimenez. Featuring a major refactor by @sudo-suhas, as well as lots of other contributors.

The Moq logo was created by Chris Ryer and is licensed under the Creative Commons Attribution 3.0 License - not used in this fork so to preserve rights.


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