Mockey

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Mockey is a simple and easy-to-use golang mock library, which can quickly and conveniently mock functions and variables. At present, it is widely used in the unit test writing of ByteDance services (7k+ repos) and is actively maintained. In essence it rewrites function instructions at runtime similarly to gomonkey.

Mockey makes it easy to replace functions, methods and variables with mocks reducing the need to specify all dependencies as interfaces.

Mockey requires inlining and compilation optimization to be disabled during compilation, or it won't work. See the FAQs for details.

It is strongly recommended to use it together with the Convey library (module dependency) in unit tests.

Install

go get github.com/bytedance/mockey@latest

Quick Guide

package main

import (
	"fmt"
	"math/rand"

	. "github.com/bytedance/mockey"
)

func main() {
	Mock(rand.Int).Return(1).Build() // mock `rand.Int` to return 1
	
	fmt.Printf("rand.Int() always return: %v\n", rand.Int())
}

Features

Mock functions and methods
- Basic
  - Simple / generic / variadic function or method (value or pointer receiver)
  - Supporting hook function
  - Supporting PatchConvey (automatically release mocks after each test case)
  - Providing GetMethod to handle special cases (e.g., exported method of unexported types, unexported method, and methods in nested structs)
- Advanced
  - Conditional mocking
  - Sequence returning
  - Decorator pattern (execute the original function after mocking)
  - Goroutine filtering (inclusion, exclusion, targeting)
  - Acquire Mocker for advanced usage (e.g., getting the execution times of target/mock function)
Mock variable
- Common variable
- Function variable

Compatibility

OS Support

Mac OS(Darwin)
Linux
Windows

Arch Support

AMD64
ARM64

Version Support

Go 1.13+

Basic Features

Simple function/method

Use Mock to mock function/method, and use Return to specify the return value:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

type A struct{}

func (a A) Foo(in string) string { return in }

type B struct{}

func (b *B) Foo(in string) string { return in }

func main() {
	// mock function
	Mock(Foo).Return("MOCKED!").Build()
	fmt.Println(Foo("anything")) // MOCKED!

	// mock method (value receiver)
	Mock(A.Foo).Return("MOCKED!").Build()
	fmt.Println(A{}.Foo("anything")) // MOCKED!

	// mock method (pointer receiver)
	Mock((*B).Foo).Return("MOCKED!").Build()
	fmt.Println(new(B).Foo("anything")) // MOCKED!
    
    // Tips: if the target has no return value, you still need to call the empty `Return()`.
}

Generic function/method

Use MockGeneric to mock generic function/method:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func FooGeneric[T any](t T) T {
	return t
}

type GenericClass[T any] struct {
}

func (g *GenericClass[T]) Foo(t T) T {
	return t
}

func main() {
	// mock generic function 
	MockGeneric(FooGeneric[string]).Return("MOCKED!").Build() // `Mock(FooGeneric[string], OptGeneric)` also works
	fmt.Println(FooGeneric("anything"))                       // MOCKED!
	fmt.Println(FooGeneric(1))                                // 1 | Not working because of type mismatch!

	// mock generic method 
	MockGeneric((*GenericClass[string]).Foo).Return("MOCKED!").Build()
	fmt.Println(new(GenericClass[string]).Foo("anything")) // MOCKED!
}

Variadic function/method

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func FooVariadic(in ...string) string {
	return in[0]
}

type A struct{}

func (a A) FooVariadic(in ...string) string { return in[0] }

func main() {
	// mock variadic function
	Mock(FooVariadic).Return("MOCKED!").Build()
	fmt.Println(FooVariadic("anything")) // MOCKED!

	// mock variadic method
	Mock(A.FooVariadic).Return("MOCKED!").Build()
	fmt.Println(A{}.FooVariadic("anything")) // MOCKED!
}

Supporting hook function

Use To to specify the hook function:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

type A struct {
	prefix string
}

func (a A) Foo(in string) string { return a.prefix + ":" + in }

func main() {
	// NOTE: hook function must have the same function signature as the original function!
	Mock(Foo).To(func(in string) string { return "MOCKED!" }).Build()
	fmt.Println(Foo("anything")) // MOCKED!

	// NOTE: for method mocking, the receiver can be added to the signature of the hook function on your need.
	Mock(A.Foo).To(func(a A, in string) string { return a.prefix + ":inner:" + "MOCKED!" }).Build()
	fmt.Println(A{prefix: "prefix"}.Foo("anything")) // prefix:inner:MOCKED!
}

Supporting `PatchConvey`

Use PatchConvey to organize test cases, just like Convey in smartystreets/goconvey. PatchConvey will automatically release the mocks after each test case:

package main_test

import (
	"testing"

	. "github.com/bytedance/mockey"
	. "github.com/smartystreets/goconvey/convey"
)

func Foo(in string) string {
	return "ori:" + in
}

func TestXXX(t *testing.T) {
    // mock 
	PatchConvey("mock 1", t, func() {
		Mock(Foo).Return("MOCKED-1!").Build() // mock 
		res := Foo("anything")                // invoke
		So(res, ShouldEqual, "MOCKED-1!")     // assert
	})

	// mock released
	PatchConvey("mock released", t, func() {
		res := Foo("anything")               // invoke
		So(res, ShouldEqual, "ori:anything") // assert
	})

	// mock again
	PatchConvey("mock 2", t, func() {
		Mock(Foo).Return("MOCKED-2!").Build() // mock 
		res := Foo("anything")                // invoke
		So(res, ShouldEqual, "MOCKED-2!")     // assert
	})
}

Providing `GetMethod` to handle special cases

Use GetMethod to get the specific method in special cases.

Mock method through an instance:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

type A struct{}

func (a A) Foo(in string) string { return in }

func main() {
	a := new(A)

	// Mock(a.Foo) won't work, because `a` is an instance of `A`, not the type `A`
	Mock(GetMethod(a, "Foo")).Return("MOCKED!").Build()
	fmt.Println(a.Foo("anything")) // MOCKED!
}

Mock exported method of unexported types:

package main

import (
	"crypto/sha256"
	"fmt"

	. "github.com/bytedance/mockey"
)

func main() {
	// `sha256.New()` returns an unexported `*digest`, whose `Sum` method is the one we want to mock
	Mock(GetMethod(sha256.New(), "Sum")).Return([]byte{0}).Build()

	fmt.Println(sha256.New().Sum([]byte("anything"))) // [0]
}

Mock unexported method:

package main

import (
	"bytes"
	"fmt"

	. "github.com/bytedance/mockey"
)

func main() {
	// `*bytes.Buffer` has an unexported `empty` method, which is the one we want to mock
	Mock(GetMethod(new(bytes.Buffer), "empty")).Return(true).Build()

	buf := bytes.NewBuffer([]byte{1, 2, 3, 4})
	b, err := buf.ReadByte()
	fmt.Println(b, err)      // 0 EOF | `ReadByte` calls `empty` method inside to check if the buffer is empty and return io.EOF
}

Mock methods in nested structs:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

type Wrapper struct {
	inner // nested struct
}

type inner struct{}

func (i inner) Foo(in string) string {
	return in
}

func main() {
	// Mock(Wrapper.Foo) won't work, because the target should be `inner.Foo`
	Mock(GetMethod(Wrapper{}, "Foo")).Return("MOCKED!").Build() // or Mock(inner.Foo).Return("MOCKED!").Build()

	fmt.Println(Wrapper{}.Foo("anything")) // MOCKED! 
    
	// Tips: `redis.Client` can be mocked in the same way as above
}

Advanced features

Conditional mocking

Use When to define multiple conditions:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return "ori:" + in
}

func main() {
	// NOTE: condition function must have the same input signature as the original function!
	Mock(Foo).
		When(func(in string) bool { return len(in) == 0 }).Return("EMPTY").
		When(func(in string) bool { return len(in) <= 2 }).Return("SHORT").
		When(func(in string) bool { return len(in) <= 5 }).Return("MEDIUM").
		Build()

	fmt.Println(Foo(""))            // EMPTY
	fmt.Println(Foo("h"))           // SHORT
	fmt.Println(Foo("hello"))       // MEDIUM
	fmt.Println(Foo("hello world")) // ori:hello world
}

Sequence returning

Use Sequence to mock multiple return values:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

func main() {
	Mock(Foo).Return(Sequence("Alice").Then("Bob").Times(2).Then("Tom")).Build()
	fmt.Println(Foo("anything")) // Alice
	fmt.Println(Foo("anything")) // Bob
	fmt.Println(Foo("anything")) // Bob
	fmt.Println(Foo("anything")) // Tom
}

Decorator pattern

Use Origin to keep the original logic of the target after mock:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return "ori:" + in
}

func main() {
	// `origin` will carry the logic of the `Foo` function
	origin := Foo

	// `decorator` will do some AOP around `origin`
	decorator := func(in string) string {
		fmt.Println("arg is", in)
		out := origin(in)
		fmt.Println("res is", out)
		return out
	}

	Mock(Foo).Origin(&origin).To(decorator).Build()

	fmt.Println(Foo("anything"))
	/*
		arg is anything
		res is ori:anything
		ori:anything
	*/
}

Goroutine filtering

Use ExcludeCurrentGoRoutine / IncludeCurrentGoRoutine / FilterGoRoutine to determine in which goroutine the mock takes effect:

package main

import (
	"fmt"
	"time"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

func main() {
	// use `ExcludeCurrentGoRoutine` to exclude current goroutine
	Mock(Foo).ExcludeCurrentGoRoutine().Return("MOCKED!").Build()
	fmt.Println(Foo("anything")) // anything | mock won't work in current goroutine

	go func() {
		fmt.Println(Foo("anything")) // MOCKED! | mock works in other goroutines
	}()

	time.Sleep(time.Second) // wait for goroutine to finish
}

Acquire `Mocker`

Acquire Mocker to use advanced features:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

func main() {
	mocker := Mock(Foo).When(func(in string) bool { return len(in) > 5 }).Return("MOCKED!").Build()
	fmt.Println(Foo("any"))      // any
	fmt.Println(Foo("anything")) // MOCKED!

	// use `MockTimes` and `Times` to track the number of times mock worked and `Foo` is called
	fmt.Println(mocker.MockTimes()) // 1
	fmt.Println(mocker.Times())     // 2

	// remock `Foo` to return "MOCKED2!"
	mocker.Return("MOCKED2!")
	fmt.Println(Foo("anything")) // MOCKED2!

	// release `Foo` mock
	mocker.Release()
	fmt.Println(Foo("anything")) // anything | mock won't work, because mock released
}

FAQ/troubleshooting

How to disable inline and compile optimization?

Command line：go test -gcflags="all=-l -N" -v ./... in tests or go build -gcflags="all=-l -N" in main packages.
Goland：use Debug or fill -gcflags="all=-l -N" in the Run/Debug Configurations > Go tool arguments dialog box.
VSCode: use Debug or add "go.buildFlags": ["-gcflags=\'all=-N -l\'"] in settings.json.

Mock doesn't work?

Inline or compilation optimizations are not disabled. Please check if this log has been printed and refer to relevant section of FAQ.
```
Mockey check failed, please add -gcflags="all=-N -l".
```
Check if Build() was not called, or that neither Return(xxx) nor To(xxx) was called, resulting in no actual effect. If the target function has no return value, you still need to call the empty Return().

Mock targets do not match exactly, as below:

package main_test

import (
	"fmt"
	"testing"

	. "github.com/bytedance/mockey"
)

type A struct{}

func (a A) Foo(in string) string { return in }

func TestXXX(t *testing.T) {
	Mock((*A).Foo).Return("MOCKED!").Build()
	fmt.Println(A{}.Foo("anything")) // won't work, because the mock target should be `A.Foo`

	a := A{}
	Mock(a.Foo).Return("MOCKED!").Build()
	fmt.Println(a.Foo("anything")) // won't work, because the mock target should be `A.Foo`
}

Please refer to Generic function/method if the target is generic. Otherwise, try to check if it hits specific cases in GetMethod.

The target function is executed in other goroutines when mock released:

package main_test

import (
	"fmt"
	"testing"
	"time"

	. "github.com/bytedance/mockey"
)

func Foo(in string) string {
	return in
}

func TestXXX(t *testing.T) {
	PatchConvey("TestXXX", t, func() {
		Mock(Foo).Return("MOCKED!").Build()
		go func() { fmt.Println(Foo("anything")) }() // the timing of executing 'Foo' is uncertain
	})
	// when the main goroutine comes here, the relevant mock has been released by 'PatchConvey'. If 'Foo' is executed before this, the mock succeeds, otherwise it fails
	fmt.Println("over")
	time.Sleep(time.Second)
}

Error "function is too short to patch"？

Inline or compilation optimizations are not disabled. Please check if this log has been printed and refer to relevant section of FAQ.
```
Mockey check failed, please add -gcflags="all=-N -l".
```
The function is really too short resulting in the compiled machine code is not long enough. Generally, two or more lines will not cause this problem. If there is such a need, you may use MockUnsafe to mock it causing unknown issues.
The function has been mocked by other tools (such as monkey etc.)

Error "re-mock , previous mock at: xxx"

The function has been mocked repeatedly in the smallest unit, as below:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

func Foo() string { return "" }

func main() {
	Mock(Foo).Return("MOCKED!").Build() // mock for the first time
	Mock(Foo).Return("MOCKED2!").Build() // mock for the second time, will panic!
	fmt.Println(Foo())
}

Please refer to PatchConvey to organize your test cases. If there is such a need, please refer to Acquire Mocker to remock.

Don't mock system functions

It is best not to directly mock system functions, as it may cause probabilistic crash issues. For example, mock time.Now will cause:

fatal error: semacquire not on the G stack

License

Mockey is distributed under the Apache License, version 2.0. The licenses of third party dependencies of Mockey are explained here.

Name		Name	Last commit message	Last commit date
Latest commit History 91 Commits
.github		.github
internal		internal
licenses		licenses
tests		tests
.gitignore		.gitignore
.golangci.yaml		.golangci.yaml
.licenserc.yaml		.licenserc.yaml
CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE-APACHE		LICENSE-APACHE
README.md		README.md
README_cn.md		README_cn.md
_typos.toml		_typos.toml
codecov.yml		codecov.yml
convey.go		convey.go
convey_test.go		convey_test.go
go.mod		go.mod
go.sum		go.sum
mock.go		mock.go
mock_condition.go		mock_condition.go
mock_condition_test.go		mock_condition_test.go
mock_generics.go		mock_generics.go
mock_generics_test.go		mock_generics_test.go
mock_sequence.go		mock_sequence.go
mock_sequence_test.go		mock_sequence_test.go
mock_test.go		mock_test.go
mock_var.go		mock_var.go
mock_var_test.go		mock_var_test.go
option.go		option.go
private.go		private.go
utils.go		utils.go
utils_test.go		utils_test.go

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Mockey

Install

Quick Guide

Features

Compatibility

OS Support

Arch Support

Version Support

Basic Features

Simple function/method

Generic function/method

Variadic function/method

Supporting hook function

Supporting `PatchConvey`

Providing `GetMethod` to handle special cases

Advanced features

Conditional mocking

Sequence returning

Decorator pattern

Goroutine filtering

Acquire `Mocker`

FAQ/troubleshooting

How to disable inline and compile optimization?

Mock doesn't work?

Error "function is too short to patch"？

Error "re-mock , previous mock at: xxx"

Don't mock system functions

License

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Releases 24

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Contributors 5

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bytedance/mockey

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Mockey

Install

Quick Guide

Features

Compatibility

OS Support

Arch Support

Version Support

Basic Features

Simple function/method

Generic function/method

Variadic function/method

Supporting hook function

Supporting PatchConvey

Providing GetMethod to handle special cases

Advanced features

Conditional mocking

Sequence returning

Decorator pattern

Goroutine filtering

Acquire Mocker

FAQ/troubleshooting

How to disable inline and compile optimization?

Mock doesn't work?

Error "function is too short to patch"？

Error "re-mock , previous mock at: xxx"

Don't mock system functions

License

About

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Resources

License

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Releases 24

Packages 0

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Contributors 5

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Supporting `PatchConvey`

Providing `GetMethod` to handle special cases

Acquire `Mocker`

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