使用gomock时可以调用EXPECT()为你的mock对象设置各种期望和返回值，用于验证期望值和运行时的值是否一致。通常情况下可以通过gomock来清晰的看出期望值和真实值的区别，但是当数据结构为指针切片时就只能看到下面这种提示，不能清晰的看出二者的区别是什么。
Got: [0xc000060610] ([]*demo.Item) Want: is equal to [0xc0000605b0] ([]*demo.Item)
可以通过设置 gomock Modifying Failure Messages的能力来优化这一点，举例如下。
// 优化前错误日志如下, 此时只能看到数据有 diff， 但不知道是什么
//--- FAIL: TestSaveToFile (1.00s)
// demo/demo.go:12: Unexpected call to *demo.MockSaver.Save([[0xc000060610]]) at demo/demo.go:12 because:
// expected call at demo/demo_test.go:14 doesn't match the argument at index 0.
// Got: [0xc000060610] ([]*demo.Item)
// Want: is equal to [0xc0000605b0] ([]*demo.Item)
// demo/controller.go:269: missing call(s) to *demo.MockSaver.Save(is equal to [0xc0000605b0] ([]*demo.Item)) demo/demo_test.go:14
// demo/controller.go:269: aborting test due to missing call(s)
func TestSaveToFile(t *testing.T) {
ctrl := gomock.NewController(t)
defer ctrl.Finish()
mockSaver := NewMockSaver(ctrl)
mockSaver.EXPECT().Save([]*Item{{Name: "bar"}})
Save(mockSaver, []*Item{{Name: "foo"}})
}
// 优化后错误日志如下，此时不仅能看到diff，也能看到差异是什么
//--- FAIL: TestSaveToFileV2 (0.00s)
// demo/demo.go:12: Unexpected call to *demo.MockSaver.Save([[0xc00009e5f0]]) at demo/demo.go:12 because:
// expected call at demo/demo_test.go:23 doesn't match the argument at index 0.
// Got: [{"Name":"foo"}]
// Want: [{"Name":"bar"}]
// demo/controller.go:269: missing call(s) to *demo.MockSaver.Save([{"Name":"bar"}]) demo/demo_test.go:23
// demo/controller.go:269: aborting test due to missing call(s)
func TestSaveToFileV2(t *testing.T) {
ctrl := gomock.NewController(t)
defer ctrl.Finish()
mockSaver := NewMockSaver(ctrl)
mockSaver.EXPECT().Save(eq([]*Item{{Name: "bar"}})) // 注意这里调用了 eq 方法
Save(mockSaver, []*Item{{Name: "foo"}})
}
func eq(want interface{}) gomock.Matcher {
return gomock.GotFormatterAdapter(
gomock.GotFormatterFunc(
func(got interface{}) string {
b, _ := json.Marshal(got)
return string(b)
},
),
gomock.WantFormatter(
gomock.StringerFunc(func() string {
b, _ := json.Marshal(want)
return string(b)
}),
gomock.Eq(want),
),
)
}