Go Mocker

Gomocker generates Golang code to easily mock a function or interface

Installing

go get github.com/jauhararifin/gomocker/gomocker

Example

1. Suppose you have an interface that look like this

type Math interface {
	Add(ctx context.Context, a, b int) (sum int, err error)
	Subtract(ctx context.Context, a, b int) (result int, err error)
}

2. Put a go generate script to generate mocker code for that interface

//go:generate gomocker gen --force --package github.com/jauhararifin/gomocker/examples github.com/jauhararifin/gomocker/examples:Math

type Math interface {
	Add(ctx context.Context, a, b int) (sum int, err error)
	Subtract(ctx context.Context, a, b int) (result int, err error)
}

3. Run go generate ./...

4. A file called math_mock_gen.go containing all the code to mock Math interface will be generated.

5. Use the mocker

func TestMathMocked_Add(t *testing.T) {
	// create the mocked `Math` and it's mocker.
	math, mocker := NewMockedMath()

	// mock the output value of `Add` method once.
	mocker.Add.MockOutputsOnce(10, nil)

	// call the Add method. 
	sum, err := math.Add(context.Background(), 17, 19)

	// it should return 10 because we mock it previously.
	assert.Nil(t, err, "wrong error")
	assert.Equal(t, 10, sum, "wrong sum")
	
	// use `mocker.Add.TakeOnceInvocation` to get the "invocation struct". The "invocation struct" contains all the
	// input and output of an invocation.
	invoc := mocker.Add.TakeOneInvocation()
	assert.Equal(t, context.Background(), invoc.Inputs.Ctx, "wrong context")
	assert.Equal(t, 17, invoc.Inputs.A, "wrong first integer")
	assert.Equal(t, 19, invoc.Inputs.B, "wrong second integer")
	assert.Equal(t, 10, invoc.Outputs.Sum, "wrong first returns")
	assert.Equal(t, nil, invoc.Outputs.Err, "wrong second returns")
}