README

gomock Build Status GoDoc

GoMock is a mocking framework for the Go programming language. It integrates well with Go's built-in testing package, but can be used in other contexts too.

Installation

Once you have installed Go, install the mockgen tool.

To get the latest released version use:

GO111MODULE=on go get github.com/golang/mock/mockgen@latest

If you use mockgen in your CI pipeline, it may be more appropriate to fixate on a specific mockgen version.

Documentation

After installing, you can use go doc to get documentation:

go doc github.com/golang/mock/gomock

Alternatively, there is an online reference for the package hosted on GoPkgDoc here.

Running mockgen

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

mockgen -source=foo.go [other options]

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:

mockgen database/sql/driver Conn,Driver

# Convenient for `go:generate`.
mockgen . Conn,Driver

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.

For an example of the use of mockgen, see the sample/ directory. In simple cases, you will need only the -source flag.

Building Mocks

type Foo interface {
  Bar(x int) int
}

func SUT(f Foo) {
 // ...
}

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)
}

Building Stubs

type Foo interface {
  Bar(x int) int
}

func SUT(f Foo) {
 // ...
}

func TestFoo(t *testing.T) {
  ctrl := gomock.NewController(t)
  defer ctrl.Finish()

  m := NewMockFoo(ctrl)

  // Does not make any assertions. Returns 101 when Bar is invoked with 99.
  m.
    EXPECT().
    Bar(gomock.Eq(99)).
    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.

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:

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:

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.

Expand ▾ Collapse ▴

Directories

Path Synopsis
gomock Package gomock is a mock framework for Go.
gomock/internal/mock_gomock Package mock_gomock is a generated GoMock package.
mockgen MockGen generates mock implementations of Go interfaces.
mockgen/internal/tests/aux_imports_embedded_interface Package bugreport is a generated GoMock package.
mockgen/internal/tests/aux_imports_embedded_interface/faux
mockgen/internal/tests/copyright_file Package empty_interface is a generated GoMock package.
mockgen/internal/tests/custom_package_name/client/v1
mockgen/internal/tests/custom_package_name/greeter
mockgen/internal/tests/custom_package_name/validator
mockgen/internal/tests/dot_imports Package dot_imports is a generated GoMock package.
mockgen/internal/tests/empty_interface Package empty_interface is a generated GoMock package.
mockgen/internal/tests/generated_identifier_conflict Package bugreport is a generated GoMock package.
mockgen/internal/tests/import_source Package mock_source is a generated GoMock package.
mockgen/internal/tests/import_source/definition Package source is a generated GoMock package.
mockgen/internal/tests/internal_pkg
mockgen/internal/tests/internal_pkg/subdir/internal/pkg
mockgen/internal/tests/internal_pkg/subdir/internal/pkg/reflect_output Package mock_pkg is a generated GoMock package.
mockgen/internal/tests/internal_pkg/subdir/internal/pkg/source_output Package mock_pkg is a generated GoMock package.
mockgen/internal/tests/mock_in_test_package
mockgen/internal/tests/performance/big_interface
mockgen/internal/tests/self_package Package core is a generated GoMock package.
mockgen/internal/tests/test_package
mockgen/internal/tests/unexported_method Package bugreport is a generated GoMock package.
mockgen/internal/tests/vendor_dep Package vendor_dep is a generated GoMock package.
mockgen/internal/tests/vendor_dep/source_mock_package Package mock_vendor_dep is a generated GoMock package.
mockgen/internal/tests/vendor_pkg Package vendor_pkg is a generated GoMock package.
mockgen/model Package model contains the data model necessary for generating mock implementations.
sample An example package with an interface.
sample/concurrent Package concurrent demonstrates how to use gomock with goroutines.
sample/concurrent/mock Package mock_concurrent is a generated GoMock package.
sample/imp1
sample/imp2
sample/imp3
sample/imp4
sample/mock_user Package mock_sample is a generated GoMock package.