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https://github.com/uber-go/mock

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

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GoMock is a mocking framework for the Go programming language.

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README 

        
# gomock



[![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.



This project originates from Google's `golang/mock` repo. Unfortunately, Google

no longer maintains this project, and given the heavy usage of gomock project

within Uber, we've decided to fork and maintain this going forward at Uber.



[Contributions](./CONTRIBUTING.md) are welcome in the form of GitHub issue or PR!



## Supported Go Versions



go.uber.org/mock supports all Go versions supported by the official

[Go Release Policy](https://go.dev/doc/devel/release#policy). That is,

the two most recent releases of Go.



## Installation



Install the `mockgen` tool.



```

go install go.uber.org/mock/mockgen@latest

```



To ensure it was installed correctly, use:



```

mockgen -version

```



If that fails, make sure your GOPATH/bin is in your PATH. You can add it with:



```

export PATH=$PATH:$(go env GOPATH)/bin

```



## Running mockgen



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



### 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]

```



### Package mode



Package mode works by specifying the package and interface names.

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`: (package mode only) Flags passed verbatim to `go list`.



- `-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.



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



- `-write_generate_directive`: Add //go:generate directive to regenerate the mock. (default false)



- `-write_source_comment`: Writes original file (source mode) or interface names (package mode) comment if true. (default true)



- `-typed`: Generate Type-safe 'Return', 'Do', 'DoAndReturn' function. (default false)



- `-exclude_interfaces`: Comma-separated names of interfaces to be excluded



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)



  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)

}

```



## Building Stubs



```go

type Foo interface {

  Bar(x int) int

}



func SUT(f Foo) {

 // ...

}



```



```go

func TestFoo(t *testing.T) {

  ctrl := gomock.NewController(t)



  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 any) 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://go.dev/

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

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

[reference-badge]:     https://pkg.go.dev/badge/go.uber.org/mock.svg

[reference]:           https://pkg.go.dev/go.uber.org/mock