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https://github.com/golang/mock

GoMock is a mocking framework for the Go programming language.
https://github.com/golang/mock

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GoMock is a mocking framework for the Go programming language.

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README 

        
# gomock



**Update, June 2023**: _This repo and tool are no longer maintained.

Please see [go.uber.org/mock](https://github.com/uber/mock) for a maintained fork instead._



[![Build Status][ci-badge]][ci-runs] [![Go Reference][reference-badge]][reference]



gomock is a mocking framework for the [Go programming language][golang]. It

integrates well with Go's built-in `testing` package, but can be used in other

contexts too.



## Installation



Once you have [installed Go][golang-install], install the `mockgen` tool.



**Note**: If you have not done so already be sure to add `$GOPATH/bin` to your

`PATH`.



To get the latest released version use:



### Go version < 1.16



```bash

GO111MODULE=on go get github.com/golang/mock/[email protected]

```



### Go 1.16+



```bash

go install github.com/golang/mock/[email protected]

```



If you use `mockgen` in your CI pipeline, it may be more appropriate to fixate

on a specific mockgen version. You should try to keep the library in sync with

the version of mockgen used to generate your mocks.



## Running mockgen



`mockgen` has two modes of operation: source and reflect.



### Source mode



Source mode generates mock interfaces from a source file.

It is enabled by using the -source flag. Other flags that

may be useful in this mode are -imports and -aux_files.



Example:



```bash

mockgen -source=foo.go [other options]

```



### Reflect mode



Reflect mode generates mock interfaces by building a program

that uses reflection to understand interfaces. It is enabled

by passing two non-flag arguments: an import path, and a

comma-separated list of symbols.



You can use "." to refer to the current path's package.



Example:



```bash

mockgen database/sql/driver Conn,Driver



# Convenient for `go:generate`.

mockgen . Conn,Driver

```



### Flags



The `mockgen` command is used to generate source code for a mock

class given a Go source file containing interfaces to be mocked.

It supports the following flags:



- `-source`: A file containing interfaces to be mocked.



- `-destination`: A file to which to write the resulting source code. If you

  don't set this, the code is printed to standard output.



- `-package`: The package to use for the resulting mock class

  source code. If you don't set this, the package name is `mock_` concatenated

  with the package of the input file.



- `-imports`: A list of explicit imports that should be used in the resulting

  source code, specified as a comma-separated list of elements of the form

  `foo=bar/baz`, where `bar/baz` is the package being imported and `foo` is

  the identifier to use for the package in the generated source code.



- `-aux_files`: A list of additional files that should be consulted to

  resolve e.g. embedded interfaces defined in a different file. This is

  specified as a comma-separated list of elements of the form

  `foo=bar/baz.go`, where `bar/baz.go` is the source file and `foo` is the

  package name of that file used by the -source file.



- `-build_flags`: (reflect mode only) Flags passed verbatim to `go build`.



- `-mock_names`: A list of custom names for generated mocks. This is specified

  as a comma-separated list of elements of the form

  `Repository=MockSensorRepository,Endpoint=MockSensorEndpoint`, where

  `Repository` is the interface name and `MockSensorRepository` is the desired

  mock name (mock factory method and mock recorder will be named after the mock).

  If one of the interfaces has no custom name specified, then default naming

  convention will be used.



- `-self_package`: The full package import path for the generated code. The

  purpose of this flag is to prevent import cycles in the generated code by

  trying to include its own package. This can happen if the mock's package is

  set to one of its inputs (usually the main one) and the output is stdio so

  mockgen cannot detect the final output package. Setting this flag will then

  tell mockgen which import to exclude.



- `-copyright_file`: Copyright file used to add copyright header to the resulting source code.



- `-debug_parser`: Print out parser results only.



- `-exec_only`: (reflect mode) If set, execute this reflection program.



- `-prog_only`: (reflect mode) Only generate the reflection program; write it to stdout and exit.



- `-write_package_comment`: Writes package documentation comment (godoc) if true. (default true)



For an example of the use of `mockgen`, see the `sample/` directory. In simple

cases, you will need only the `-source` flag.



## Building Mocks



```go

type Foo interface {

  Bar(x int) int

}



func SUT(f Foo) {

 // ...

}



```



```go

func TestFoo(t *testing.T) {

  ctrl := gomock.NewController(t)



  // Assert that Bar() is invoked.

  defer ctrl.Finish()



  m := NewMockFoo(ctrl)



  // Asserts that the first and only call to Bar() is passed 99.

  // Anything else will fail.

  m.

    EXPECT().

    Bar(gomock.Eq(99)).

    Return(101)



  SUT(m)

}

```



If you are using a Go version of 1.14+, a mockgen version of 1.5.0+, and are

passing a *testing.T into `gomock.NewController(t)` you no longer need to call

`ctrl.Finish()` explicitly. It will be called for you automatically from a self

registered [Cleanup](https://pkg.go.dev/testing?tab=doc#T.Cleanup) function.



## Building Stubs



```go

type Foo interface {

  Bar(x int) int

}



func SUT(f Foo) {

 // ...

}



```



```go

func TestFoo(t *testing.T) {

  ctrl := gomock.NewController(t)

  defer ctrl.Finish()



  m := NewMockFoo(ctrl)



  // Does not make any assertions. Executes the anonymous functions and returns

  // its result when Bar is invoked with 99.

  m.

    EXPECT().

    Bar(gomock.Eq(99)).

    DoAndReturn(func(_ int) int {

      time.Sleep(1*time.Second)

      return 101

    }).

    AnyTimes()



  // Does not make any assertions. Returns 103 when Bar is invoked with 101.

  m.

    EXPECT().

    Bar(gomock.Eq(101)).

    Return(103).

    AnyTimes()



  SUT(m)

}

```



## Modifying Failure Messages



When a matcher reports a failure, it prints the received (`Got`) vs the

expected (`Want`) value.



```shell

Got: [3]

Want: is equal to 2

Expected call at user_test.go:33 doesn't match the argument at index 1.

Got: [0 1 1 2 3]

Want: is equal to 1

```



### Modifying `Want`



The `Want` value comes from the matcher's `String()` method. If the matcher's

default output doesn't meet your needs, then it can be modified as follows:



```go

gomock.WantFormatter(

  gomock.StringerFunc(func() string { return "is equal to fifteen" }),

  gomock.Eq(15),

)

```



This modifies the `gomock.Eq(15)` matcher's output for `Want:` from `is equal

to 15` to `is equal to fifteen`.



### Modifying `Got`



The `Got` value comes from the object's `String()` method if it is available.

In some cases the output of an object is difficult to read (e.g., `[]byte`) and

it would be helpful for the test to print it differently. The following

modifies how the `Got` value is formatted:



```go

gomock.GotFormatterAdapter(

  gomock.GotFormatterFunc(func(i interface{}) string {

    // Leading 0s

    return fmt.Sprintf("%02d", i)

  }),

  gomock.Eq(15),

)

```



If the received value is `3`, then it will be printed as `03`.



[golang]:              http://golang.org/

[golang-install]:      http://golang.org/doc/install.html#releases

[gomock-reference]:    https://pkg.go.dev/github.com/golang/mock/gomock

[ci-badge]:            https://github.com/golang/mock/actions/workflows/test.yaml/badge.svg

[ci-runs]:             https://github.com/golang/mock/actions

[reference-badge]:     https://pkg.go.dev/badge/github.com/golang/mock.svg

[reference]:           https://pkg.go.dev/github.com/golang/mock



## Debugging Errors



### reflect vendoring error



```text

cannot find package "."

... github.com/golang/mock/mockgen/model

```



If you come across this error while using reflect mode and vendoring

dependencies there are three workarounds you can choose from:



1. Use source mode.

2. Include an empty import `import _ "github.com/golang/mock/mockgen/model"`.

3. Add `--build_flags=--mod=mod` to your mockgen command.



This error is due to changes in default behavior of the `go` command in more

recent versions. More details can be found in

[#494](https://github.com/golang/mock/issues/494).