Mockable interface methods in Go, maybe

main.go

type InterfaceThing interface {
	MockableMethod() int
	TalksToMockableMethod() bool
}

func MockableMethod() int {
	// i do things that are annoying to test, like run exec.Cmd or talk to a database!
	
	return 0
}

// implements part of the interface
type ParentThingWithMockableMethod struct {
	mockableMethod func() int
}

func (t *ParentThingWithMockableMethod) MockableMethod() int {
	return t.mockableMethod()
}

// implements the whole interface, with Parent's MockableMethod
type ChildThing struct {
	ParentThingWithMockableMethod
}

func NewChildThing() *ChildThing {
	thing := &ChildThing{}
	thing.mockableMethod = MockableMethod
	
	return thing
}

func (c *ChildThing) TalksToMockableMethod() bool {
	return c.MockableMethod() > 0
}

main_test.go

func TestTalksToMockableMethod(t *testing.T) {
	thing := ChildThing{
		ParentThingWithMockableMethod{
			mockableMethod: func() { return 1 }
		}
	}
	assert.True(t, thing.TalksToMockableMethod())
	
	thing.mockableMethod = func() { return -1 }
	assert.False(t, thing.TalksToMockableMethod())
}