Mockey

English | 中文

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 monkey or 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 goconvey library in unit tests.

Install

go get github.com/bytedance/mockey@latest

Quick Guide

Simplest example

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()) // Try if it's still random?
}

Unit test example

package main_test

import (
	"math/rand"
	"testing"

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

// Win function to be tested, input a number, win if it's greater than random number, otherwise lose
func Win(in int) bool {
	return in > rand.Int()
}

func TestWin(t *testing.T) {
	PatchConvey("TestWin", t, func() {
		Mock(rand.Int).Return(100).Build() // mock
		
		res1 := Win(101)                   // execute
		So(res1, ShouldBeTrue)             // assert
		
		res2 := Win(99)         // execute
		So(res2, ShouldBeFalse) // assert
	})
}

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, use Return to specify the return value, and use Build to make the mock effective:

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()` or use `To` to customize the hook function.
}

Generic function/method

Starting from mockey v1.3.0, Mock experimentally adds the ability to automatically identify generics (for go1.20+), you can use Mock to directly replace MockGeneric

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!
}

Additionally, Golang generics share implementation for different types with the same underlying type. For example, in type MyString string, MyString and string share one implementation. Therefore, mocking one type will interfere with the other. To further distinguish, you need to use GenericInfo to determine the specific type:

package main

import (
	"fmt"

	. "github.com/bytedance/mockey"
)

type MyString string

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

func main() {
	MockGeneric(FooGeneric[string]).Return("MOCKED!").Build()
	fmt.Println(FooGeneric("anything"))           // MOCKED!
	fmt.Println(FooGeneric[MyString]("anything")) // MOCKED! | This is due to interference after mocking the string type
}

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 (if the receiver is not used, it can be omitted, and mockey is compatible).
	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`

It is recommended to use PatchConvey to organize test cases, just like Goconvey in smartystreets/goconvey. PatchConvey will automatically release the mocks after each test case, eliminating the need for defer, i.e., the mock scope is only within PatchConvey:

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
	})
    
    // Tips: Like `Convey`, `PatchConvey` can be nested; each layer of `PatchConvey` will only release its own internal mocks
}

Providing `GetMethod` to handle special cases

In special cases where direct mocking is not possible or not effective, you can use GetMethod to get the corresponding method before mocking. Please ensure that the passed object is not nil.

Mock method through an instance (including interface type instances):

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`
	// Tips: if the instance is an interface type, you can use it the same way
	// var ia interface{ Foo(string) string } = new(A)
	// Mock(GetMethod(ia, "Foo")).Return("MOCKED!").Build()
	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]
	
	// Tips: this is a special case of "mocking methods through instances", where the type corresponding to the instance is unexported
}

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! 
}

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

By default, mocks take effect in all goroutines. You can use the following APIs to specify in which goroutines the mock takes effect:

IncludeCurrentGoRoutine: Only takes effect in the current goroutine
ExcludeCurrentGoRoutine: Takes effect in all goroutines except the current one
FilterGoRoutine: Include or exclude specified goroutines (by goroutine id)

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
	
	// Tips: You can use `GetGoroutineId` to get the current goroutine ID
}

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

	// Tips: When remocking or releasing mock, the related counters will be reset to 0.

	// remock `Foo` to return "MOCKED2!"
	mocker.Return("MOCKED2!")
	fmt.Println(Foo("anything")) // MOCKED2!
	fmt.Println(mocker.MockTimes()) // 1 | Reset to 0 when remocking

	// release `Foo` mock
	mocker.Release()
	fmt.Println(Foo("anything")) // anything | mock won't work, because mock released
	fmt.Println(mocker.MockTimes()) // 0 | Reset to 0 when releasing
}

FAQ

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)
}

The function call happens before mock execution. Try setting a breakpoint at the first line of the original function. If the execution reaches the first line when the stack is not after the mock code in the unit test, this is the issue. Common in init() functions. See relevant section for how to mock functions in init().
Using non-generic mock for generic functions. See Generic function/method section for details.

What is the execution order of nested PatchConvey?

Completely consistent with Convey, please refer to the goconvey related documentation.

How to mock interface types?

Method 1: Use GetMethod to get the corresponding method from the instance

package main

import (
   "fmt"

   . "github.com/bytedance/mockey"
)

type FooI interface {
   Foo(string) string
}

func NewFoo() FooI {
   return &foo{}
}

// foo the original implementation of 'FooI'
type foo struct{}

func (f *foo) Foo(in string) string {
   return in
}

func main() {
   // get the original implementation and mock it
   instance := NewFoo()
   Mock(GetMethod(instance, "Foo")).Return("MOCKED!").Build()

   fmt.Println(instance.Foo("anything")) // MOCKED!
}

Method 2: Create a dummy implementation type and mock the corresponding constructor to return that type

package main

import (
   "fmt"

   . "github.com/bytedance/mockey"
)

type FooI interface {
   Foo(string) string
}

func NewFoo() FooI {
   return &foo{}
}

// foo the original implementation of 'FooI'
type foo struct{}

func (f *foo) Foo(in string) string {
   return in
}

func main() {
   // generate a dummy implementation of 'FooI' and mock it
   type foo struct{ FooI }
   Mock((*foo).Foo).Return("MOCKED!").Build()
   // mock the constructor of 'FooI' to return the dummy implementation
   Mock(NewFoo).Return(new(foo)).Build()

   fmt.Println(NewFoo().Foo("anything")) // MOCKED!
}

How to mock functions in dependency package init()?

We often encounter this problem: there is an init function in the dependency package that panics when executed in local or CI environment, causing unit tests to fail directly. We hope to mock the panicking function, but since init functions execute before unit tests, general methods cannot succeed.

Suppose package a references package b, and package b's init runs a function FunC from package c. We hope to mock FunC before package a's unit test starts. Since golang's init order is dictionary order, we just need to initialize a package d with mock functions before package c's init. Here's a solution:

Create a new package d, then create an init function in this package to mock FunC; Special attention: you need to check for CI environment (such as os.Getenv("ENV") == "CI"), otherwise the production environment will also be mocked
In package a's "first go file in dictionary order", "additionally reference" package d, and make package d's reference at the front of all imports
Inject ENV == "CI" when running unit tests to make the mock effective

Troubleshooting

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 or gomonkey etc.)

Error "invalid memory address or nil pointer dereference"？

This is most likely an issue with your business code or test code. It is recommended to debug step by step or check for uninitialized objects. It is generally common in the following situations:

type Loader interface{ Foo() }
var loader Loader
loader.Foo() // invalid memory address or nil pointer dereference

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())
}

For a function, it can only be mocked once in a PatchConvey (even without PatchConvey). Please refer to PatchConvey to organize your test cases. If there is such a need, please refer to Acquire Mocker to remock.

If you encounter this error when mocking the same generic function with different type arguments, it may be caused by the fact that the gcshape of different arguments is the same. For details, see the Generic function/method section.

Error "args not match" / "Return Num of Func a does not match" / "Return value idx of rets can not convertible to"?

If using Return, check if the return parameters are consistent with the target function's return values
If using To, check if the input and output parameters are consistent with the target function
If using When, check if the input parameters are consistent with the target function
If the target and hook function signatures appear identical in the error, check if the import packages in the test code and target function code are consistent

Crash "signal SIGBUS: bus error"?

Mac M series computers (darwin/arm64) have a higher probability of encountering this issue. You can retry multiple times. Currently, there is no elegant solution. Related discussion here.

fatal error: unexpected signal during runtime execution
[signal SIGBUS: bus error code=0x1 addr=0x10509aec0 pc=0x10509aec0]

Crash "signal SIGSEGV: segmentation violation"?

Lower version MacOS (10.x / 11.x) may have the following error. Currently, you can temporarily resolve it by disabling cgo with go env -w CGO_ENABLED=0:

fatal error: unexpected signal during runtime execution
[signal SIGSEGV: segmentation violation code=0x1 addr=0xb01dfacedebac1e pc=0x7fff709a070a]

Crash "semacquire not on the G stack"?

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

fatal error: semacquire not on the G stack

M series Mac + Go 1.18 goes to wrong branch?

This is a bug in golang under arm64 architecture for specific versions. Please check if the golang version is 1.18.1～1.18.5. If so, upgrade the golang version.

Golang fix MR:

Error "mappedReady and other memstats are not equal" / "index out of range" / "invalid reference to runtime.sysAlloc"？

The version is too old, please upgrade to the latest version of mockey.

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 118 Commits
.github		.github
internal		internal
licenses		licenses
.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_caller_test.go		mock_caller_test.go
mock_condition.go		mock_condition.go
mock_condition_test.go		mock_condition_test.go
mock_generics.go		mock_generics.go
mock_generics_1.20_test.go		mock_generics_1.20_test.go
mock_generics_below_1.20_test.go		mock_generics_below_1.20_test.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

License

bytedance/mockey

Folders and files

Latest commit

History

Repository files navigation

Mockey

Install

Quick Guide

Simplest example

Unit test example

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

How to disable inline and compile optimization?

Mock doesn't work?

What is the execution order of nested PatchConvey?

How to mock interface types?

How to mock functions in dependency package init()?

Troubleshooting

Error "function is too short to patch"？

Error "invalid memory address or nil pointer dereference"？

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

Error "args not match" / "Return Num of Func a does not match" / "Return value idx of rets can not convertible to"?

Crash "signal SIGBUS: bus error"?

Crash "signal SIGSEGV: segmentation violation"?

Crash "semacquire not on the G stack"?

M series Mac + Go 1.18 goes to wrong branch?

Error "mappedReady and other memstats are not equal" / "index out of range" / "invalid reference to runtime.sysAlloc"？

License

About

Topics

Resources

License

Code of conduct

Contributing

Uh oh!

Stars

Watchers

Forks

Releases 29

Packages 0

Uh oh!

Contributors 6

Uh oh!

Languages

Supporting `PatchConvey`

Providing `GetMethod` to handle special cases

Acquire `Mocker`

Packages