TL;DR: mocked method accepts closure. I wonder how to create custom matcher (https://godoc.org/github.com/golang/mock/gomock#Matcher): closure itself in turn is working with private structure - meaning I can't even call the closure in my test to check it against expectations.
I'm working on a small app using Slack API with help of nlopes/slack (https://github.com/nlopes/slack).
For testing, I'm mocking nlopes/slack with gomock. For that I've created interface
type slackAPI interface {
OpenConversation(*slack.OpenConversationParameters) (*slack.Channel, bool, bool, error)
PostMessage(channelID string, options ...slack.MsgOption) (string, string, error)
GetUserByEmail(email string) (*slack.User, error)
}
I have no problem testing OpenConversation or GetUserByEmail, e.g.
slackAPIClient.
EXPECT().
GetUserByEmail("some#email.com").
Return(slackUserJohndoe, nil).
Times(1)
Things get more complicated when it comes to PostMessage. In main code the call looks like
_, _, err := slackAPIClient.PostMessage(channel.ID, slack.MsgOptionText(message, false))
And slack.MsgOptionText (from nlopes/slack) is actually returning closure:
func MsgOptionText(text string, escape bool) MsgOption {
return func(config *sendConfig) error {
if escape {
text = slackutilsx.EscapeMessage(text)
}
config.values.Add("text", text)
return nil
}
}
Since method is accepting closure, I need to create custom gomock matcher (https://godoc.org/github.com/golang/mock/gomock#Matcher). Custom matcher itself is not a problem, it would look something like
type higherOrderFunctionEqMatcher struct {
x interface{}
}
func (e hofEqMatcher) Matches(x interface{}) bool {
//return m.x == x
return true
}
func (e hofEqMatcher) String(x interface{}) string {
return fmt.Sprintf("is equal %v", e.x)
}
However, since MsgOptionText uses nlopes/slack private structure sendConfig, I wonder how can I even work with that in scope of my test to check equality to expectations.
How should I tackle such problem?
Bearing in mind that
in Golang you can't compare functions
in this precise case I can't do indirect test by calling closure itself (since it's using private 3rd party lib's structure as an argument)
the solution I've found is to mock slack.MsgOptionText(message, false), which in turn returns closure for PostMessage(channelID string, options ...slack.MsgOption):
type slackMsgCreator interface {
MsgOptionText(string, bool) slack.MsgOption
}
type slackMsgCreatorInst struct{}
func (s slackMsgCreatorInst) MsgOptionText(text string, escape bool) slack.MsgOption {
return slack.MsgOptionText(text, escape)
}
...
slackMsgCreator.
EXPECT().
MsgOptionText("Dear John Doe, message goes here", false).
Return(slack.MsgOptionText("Dear John Doe, message goes here", false)).
Times(1)
And, as for PostMessage - as was advised in comments, the only thing that I could check is that closure is not nil:
slackAPIClient.
EXPECT().
PostMessage("ABCDE", Not(Nil())).
AnyTimes()
Related
I am trying to create a database mock in my code, then i am introducing interfaces to my code, to create the mock:
This is my code (I don't know if it's the correct approach)
package interfaces
type ObjectAPI interface {
FindSomethingInDatabase(ctx context.Context, name string) (e.Response, error)
}
And my implementation of the interface is:
package repositories
func FindSomethingInDatabase(ctx context.Context, name string) (e.Response, error) {
statement, err := db.SqlStatementWithCtx(ctx,
`SELECT *
FROM table
WHERE name = ? LIMIT 1`)
row := statement.QueryRowContext(ctx, name)
if err != nil {
return e.Response{}, err
}
statement.Close()
return toResponse(row), nil //this method convert row database to e.Response struct
}
Now I need call from one method the implementation of my FindSomethingInDatabase, then i am receiving an object type interface:
func CallImplementation(request *dto.XRequest, repo i.ObjectAPI) dto.XResponse{
result := repo.FindSomethingInDatabase(request.Ctx, request.Name)
// more code
}
But now I don't know how can I call CallImplementation` to pass an object with the implementation.
Call the method passing the implementation of the interface
An interface describes a type. Since your FindSomethingInDatabase implementation is just a func without a receiver, there is no type that implements interface ObjectAPI.
You can pass a value of type func(ctx context.Context, name string) (e.Response, error) into CallImplementation as a callback and get rid of the interface altogether. Alternatively, keep the interface, define a type, and make that type the receiver for your current FindSomethingInDatabase implementation. You can then pass the type to CallImplementation, since it will now implement the ObjectAPI interface. An example of the latter (which would be my preferred option for extensibility):
type database struct {}
func (d *database) FindSomethingInDatabase(ctx context.Context, name string) (e.Response, error) {
// ...
}
func CallImplementation(request *dto.XRequest, repo i.ObjectAPI) dto.XResponse{
result := repo.FindSomethingInDatabase(request.Ctx, request.Name)
// more code
}
func main() {
db := &database{}
_ = Callimplementation(getRequest(), db)
}
In this case, you will probably want to store db as a member of database, rather than having it as a global variable (which appears to be the case now).
refer mockery. it provides auto generation of mocks for interfaces and can be good reference about best practices for mocking.
typically you would do this:
api.go:
type API interface {
Something(ctx context.Context, name string) (e.Response, error)
}
type ApiImpl struct {
}
func (t *ApiImpl) Something(ctx context.Context, name string) (e.Response, error) {
// impl
}
api_test.go
// mocks can be hand coded or autogenerated using mockery
type MockImpl struct {
}
func (m *MockImpl) Something(ctx context.Context, name string) (e.Response, error) {
// mock implementation
}
func TestSomething(t * testing.T) {
// test code with mocks
}
I have a function that parses different fields in the array of type ValidationError to generate custom error messages something like the following function.
func foo(err validator.ValidationErrors) []string {
var errStr []string
for _, e := range err {
tag := e.Tag()
field := e.Field()
errStr = append(errStr, tag + ":" + field)
}
return errStr
}
I want to write unit test for this function to ensure that the custom message is as expected. How can I mock a variable of type validator.ValidationError. Below is the structure of ValidationError:
type ValidationErrors []FieldError
FieldError is an interface which contains functions (such as Tag(), Field(), etc.) to get error details.
If you want to unit-test a function that takes validator.ValidationErrors, just construct the test value yourself, using a type (possibly a struct) that implements FieldError.
The methods are not many, but if you want to implement only those that your function calls, you can embed validator.FieldError in the struct type:
type mockFieldError struct {
validator.FieldError
tag string
field string
}
func (e mockFieldError) Tag() string { return e.tag }
func (e mockFieldError) Field() string { return e.field }
And construct validator.ValidationErrors (note that the embedded validator.FieldError is uninitialized, so make sure the function under test doesn't call other methods you didn't implement, or it will panic):
ve := validator.ValidationErrors{
mockFieldError{tag: "a", field: "field1"},
mockFieldError{tag: "b", field: "field2"},
}
So now calling foo with the above value compiles and returns a string that you can assert against your expected output:
s := foo(ve)
fmt.Println(s) // [a:field1 b:field2]
Full playground: https://go.dev/play/p/-btZ6lrKk4V
I'm trying to test the following method:
//AuthenticationMiddleware Middleware which handles all of the authentication.
func AuthenticationMiddleware(context context.ContextIntf, w web.ResponseWriter, r *web.Request, next web.NextMiddlewareFunc) {
//Check if url is one that doesn't need authorization. If not than send them to the login page.
for _, url := range AuthMWInstance.GetInfo().nonAuthURLs {
if url.Method == r.Method && strings.Contains(r.URL.Path, url.DomainName) {
next(w, r)
return
}
}
if errSt := CheckForAuthorization(context, r, w); errSt != nil {
responses.Write(w, responses.Unauthorized(*errSt))
return
}
defer context.GetInfo().Session.SessionRelease(w)
next(w, r)
}
In this case, there's a SessionRelease that gets invoked iff r contains a URL that requires authorization, and that authorization was successful.
It may be important to know that :
type MiddlewareSt struct {
//NonAuthUrls URLs that can be accessed without a token.
nonAuthURLs []url.URLSt
}
type MiddlewareIntf interface {
GetInfo() *MiddlewareSt
CheckTokenAndSetSession(context context.ContextIntf, r *web.Request, w web.ResponseWriter,
token string, scope string, remoteAddr string) *errors.ErrorSt
}
var AuthMWInstance MiddlewareIntf
and that CheckForAuthorization's return value ultimately relies upon AuthMWInstance
My Test Strategy
Create a stub middleware instance to initialize AuthMWInstance to, that simply returns nil for CheckTokenAndSetSession (with the session setting abstracted out, of course, to the creation of the stub object itself, which has the Session), and a MiddlewareSt full of fake nonAuthURLs for GetInfo()
Create a mock session.Store that, for all tests except the Sanity Test, expects zero calls to SessionRelease.
It's probably worth noting (but assumed) that I'm using testify,mockery libraries for the mocking and the assertion stuff.
The test
Is implemented thus:
func TestAuthenticationMiddleware(t *testing.T) {
// bring in the errors
sdkTesting.InitErrors()
// create/set up the test doubles
// mock session
sessionMock := new(testing_mock.MockStore)
// temporarily set AuthMWInstance to a stub
instance := AuthMWInstance
AuthMWInstance = &StubMiddlewareInstance{
Session: sessionMock,
}
// AuthMWInstance.Session
defer func() { AuthMWInstance = instance }()
// fake ResponseWriter
w := new(StubResponseWriter)
// fake web requests
requestWithoutAuth := new(web.Request)
requestWithoutAuth.Request = httptest.NewRequest("GET",
"http://example.com/logout",
nil,
)
// do tests here
t.Run("AuthorizationNotRequired", func(t *testing.T) {
// place expectations on sessionMock, namely that it does
// **not** invoke `SessionRelease`
sessionMock.On("SessionRelease", w).
Times(0)
AuthenticationMiddleware(new(context.Context),
w,
requestWithoutAuth,
web.NextMiddlewareFunc(func(web.ResponseWriter, *web.Request) {}))
sessionMock.AssertExpectations(t)
})
}
Runtime behavior
The following false fail happens: . It's literally as if, instead of doing:
sessionMock.On("SessionRelease", w).
Times(0)
, I was like:
sessionMock.On("SessionRelease", w).
Once()
NOTE session.Store.SessionRelease does not return anything, hence why I didn't even bother using Return().
Am I asserting that it is to be called exactly zero times right?
I feel a bit silly for this.
The problem was that I was bothering with
sessionMock.AssertExpectations(t)
when I could have simply said
sessionMock.AssertNotCalled(t, "SessionRelease", w)
(Documentation on that method here)
Doing the latter resolved the issue, and did exactly what I was trying to accomplish.
I have a function which is getting called inside other function.
send_api.go
function *send_api*(client *http.Client,url string) map[string]string,error {
//send api request and parse the response and return the dict
return dictmap
for eg:{apple fruit}
}
Then this function is getting called in main() function
func *main()*{
getmap :=send_api(client *http.Client,"test.com")
}
good.go
func *get_dict_key*(key string) string,error {
value,ok := get_map[key]
if !ok {
return fmt.Errorf("value is nil")
}
return value ,nil
}
function *good*(client *http.client, key string) {
//get a dictionary value
dcmap,err := get_dict_key("apple")
if err != nil {
panic(err)
}
value := dcmap[key]
//use the value to do other processing
}
unit_test
func Test_good(t *testing.T) {
Convey("AND quadra and conusl dcs are mapped",t, func() {
mockResponses := send mock GET request to the URL and receive a response{"apple":"fruit"}
}
server, client := tools.TestClientServer(&mockResponses)
defer server.Close()
getMap := send_api(client.HTTPClient, "http://test")
//At this point getMAP has value {'apple' 'fruit'}
**q1.How to pass getMap value inside this get_dict_fkey function during testing?**
value := get_dict_key("apple")
good(client,"apple") #error:(value is nil)
Q1. **q1.How to pass getMap value inside this get_dict_function during testing?*
Any pointer would be helpful?
Assuming you are facing difficulty to mock http.Client, I would like to suggest following options.
1. Refactor the code
You need to refactor the code in such a way that you can pass the mockable dependencies to function that you would like to test.
For example,
Refactor func send_api(client *http.Client,url string) map[string]string,error so that it does api request and getting/parsing data, but call another function from it, which does the further processing (that actually you would like to test and not the http.Client part).
But, with this approach, you may not be able to test end to end flow. But you can test those functions separately.
2. Mock http.Client
Again, you may need to refactor your code. Some related article can be found here
Update: Recommending to watch justforfunc #16: unit testing HTTP servers
I'm puzzled with dependencies. I want to be able to replace some function calls with mock ones. Here's a snippet of my code:
func get_page(url string) string {
get_dl_slot(url)
defer free_dl_slot(url)
resp, err := http.Get(url)
if err != nil { return "" }
defer resp.Body.Close()
contents, err := ioutil.ReadAll(resp.Body)
if err != nil { return "" }
return string(contents)
}
func downloader() {
dl_slots = make(chan bool, DL_SLOT_AMOUNT) // Init the download slot semaphore
content := get_page(BASE_URL)
links_regexp := regexp.MustCompile(LIST_LINK_REGEXP)
matches := links_regexp.FindAllStringSubmatch(content, -1)
for _, match := range matches{
go serie_dl(match[1], match[2])
}
}
I'd like to be able to test downloader() without actually getting a page through http - i.e. by mocking either get_page (easier since it returns just the page content as a string) or http.Get().
I found this thread which seems to be about a similar problem. Julian Phillips presents his library, Withmock as a solution, but I'm unable to get it to work. Here's the relevant parts of my testing code, which is largely cargo cult code to me, to be honest:
import (
"testing"
"net/http" // mock
"code.google.com/p/gomock"
)
...
func TestDownloader (t *testing.T) {
ctrl := gomock.NewController()
defer ctrl.Finish()
http.MOCK().SetController(ctrl)
http.EXPECT().Get(BASE_URL)
downloader()
// The rest to be written
}
The test output is following:
ERROR: Failed to install '_et/http': exit status 1 output: can't load
package: package _et/http: found packages http (chunked.go) and main
(main_mock.go) in
/var/folders/z9/ql_yn5h550s6shtb9c5sggj40000gn/T/withmock570825607/path/src/_et/http
Is the Withmock a solution to my testing problem? What should I do to get it to work?
Personally, I don't use gomock (or any mocking framework for that matter; mocking in Go is very easy without it). I would either pass a dependency to the downloader() function as a parameter, or I would make downloader() a method on a type, and the type can hold the get_page dependency:
Method 1: Pass get_page() as a parameter of downloader()
type PageGetter func(url string) string
func downloader(pageGetterFunc PageGetter) {
// ...
content := pageGetterFunc(BASE_URL)
// ...
}
Main:
func get_page(url string) string { /* ... */ }
func main() {
downloader(get_page)
}
Test:
func mock_get_page(url string) string {
// mock your 'get_page()' function here
}
func TestDownloader(t *testing.T) {
downloader(mock_get_page)
}
Method2: Make download() a method of a type Downloader:
If you don't want to pass the dependency as a parameter, you could also make get_page() a member of a type, and make download() a method of that type, which can then use get_page:
type PageGetter func(url string) string
type Downloader struct {
get_page PageGetter
}
func NewDownloader(pg PageGetter) *Downloader {
return &Downloader{get_page: pg}
}
func (d *Downloader) download() {
//...
content := d.get_page(BASE_URL)
//...
}
Main:
func get_page(url string) string { /* ... */ }
func main() {
d := NewDownloader(get_page)
d.download()
}
Test:
func mock_get_page(url string) string {
// mock your 'get_page()' function here
}
func TestDownloader() {
d := NewDownloader(mock_get_page)
d.download()
}
If you change your function definition to use a variable instead:
var get_page = func(url string) string {
...
}
You can override it in your tests:
func TestDownloader(t *testing.T) {
get_page = func(url string) string {
if url != "expected" {
t.Fatal("good message")
}
return "something"
}
downloader()
}
Careful though, your other tests might fail if they test the functionality of the function you override!
The Go authors use this pattern in the Go standard library to insert test hooks into code to make things easier to test:
https://golang.org/src/net/hook.go
https://golang.org/src/net/dial.go#L248
https://golang.org/src/net/dial_test.go#L701
I'm using a slightly different approach where public struct methods implement interfaces but their logic is limited to just wrapping private (unexported) functions which take those interfaces as parameters. This gives you the granularity you would need to mock virtually any dependency and yet have a clean API to use from outside your test suite.
To understand this it is imperative to understand that you have access to the unexported methods in your test case (i.e. from within your _test.go files) so you test those instead of testing the exported ones which have no logic inside beside wrapping.
To summarize: test the unexported functions instead of testing the exported ones!
Let's make an example. Say that we have a Slack API struct which has two methods:
the SendMessage method which sends an HTTP request to a Slack webhook
the SendDataSynchronously method which given a slice of strings iterates over them and calls SendMessage for every iteration
So in order to test SendDataSynchronously without making an HTTP request each time we would have to mock SendMessage, right?
package main
import (
"fmt"
)
// URI interface
type URI interface {
GetURL() string
}
// MessageSender interface
type MessageSender interface {
SendMessage(message string) error
}
// This one is the "object" that our users will call to use this package functionalities
type API struct {
baseURL string
endpoint string
}
// Here we make API implement implicitly the URI interface
func (api *API) GetURL() string {
return api.baseURL + api.endpoint
}
// Here we make API implement implicitly the MessageSender interface
// Again we're just WRAPPING the sendMessage function here, nothing fancy
func (api *API) SendMessage(message string) error {
return sendMessage(api, message)
}
// We want to test this method but it calls SendMessage which makes a real HTTP request!
// Again we're just WRAPPING the sendDataSynchronously function here, nothing fancy
func (api *API) SendDataSynchronously(data []string) error {
return sendDataSynchronously(api, data)
}
// this would make a real HTTP request
func sendMessage(uri URI, message string) error {
fmt.Println("This function won't get called because we will mock it")
return nil
}
// this is the function we want to test :)
func sendDataSynchronously(sender MessageSender, data []string) error {
for _, text := range data {
err := sender.SendMessage(text)
if err != nil {
return err
}
}
return nil
}
// TEST CASE BELOW
// Here's our mock which just contains some variables that will be filled for running assertions on them later on
type mockedSender struct {
err error
messages []string
}
// We make our mock implement the MessageSender interface so we can test sendDataSynchronously
func (sender *mockedSender) SendMessage(message string) error {
// let's store all received messages for later assertions
sender.messages = append(sender.messages, message)
return sender.err // return error for later assertions
}
func TestSendsAllMessagesSynchronously() {
mockedMessages := make([]string, 0)
sender := mockedSender{nil, mockedMessages}
messagesToSend := []string{"one", "two", "three"}
err := sendDataSynchronously(&sender, messagesToSend)
if err == nil {
fmt.Println("All good here we expect the error to be nil:", err)
}
expectedMessages := fmt.Sprintf("%v", messagesToSend)
actualMessages := fmt.Sprintf("%v", sender.messages)
if expectedMessages == actualMessages {
fmt.Println("Actual messages are as expected:", actualMessages)
}
}
func main() {
TestSendsAllMessagesSynchronously()
}
What I like about this approach is that by looking at the unexported methods you can clearly see what the dependencies are. At the same time the API that you export is a lot cleaner and with less parameters to pass along since the true dependency here is just the parent receiver which is implementing all those interfaces itself. Yet every function is potentially depending only on one part of it (one, maybe two interfaces) which makes refactors a lot easier. It's nice to see how your code is really coupled just by looking at the functions signatures, I think it makes a powerful tool against smelling code.
To make things easy I put everything into one file to allow you to run the code in the playground here but I suggest you also check out the full example on GitHub, here is the slack.go file and here the slack_test.go.
And here the whole thing.
I would do something like,
Main
var getPage = get_page
func get_page (...
func downloader() {
dl_slots = make(chan bool, DL_SLOT_AMOUNT) // Init the download slot semaphore
content := getPage(BASE_URL)
links_regexp := regexp.MustCompile(LIST_LINK_REGEXP)
matches := links_regexp.FindAllStringSubmatch(content, -1)
for _, match := range matches{
go serie_dl(match[1], match[2])
}
}
Test
func TestDownloader (t *testing.T) {
origGetPage := getPage
getPage = mock_get_page
defer func() {getPage = origGatePage}()
// The rest to be written
}
// define mock_get_page and rest of the codes
func mock_get_page (....
And I would avoid _ in golang. Better use camelCase
the simplest way is to set function into a global variable and before test set your custom method
// package base36
func GenerateRandomString(length int) string {
// your real code
}
// package teamManager
var RandomStringGenerator = base36.GenerateRandomString
func (m *TeamManagerService) CreateTeam(ctx context.Context) {
// we are using the global variable
code = RandomStringGenerator(5)
// your application logic
return nil
}
and in your test, you must first mock that global variable
teamManager.RandomStringGenerator = func(length int) string {
return "some string"
}
service := &teamManager.TeamManagerService{}
service.CreateTeam(context.Background())
// now when we call any method that user teamManager.RandomStringGenerator, it will call our mocked method
another way is to pass RandomStringGenerator as a dependency and store it inside TeamManagerService and use it like this:
// package teamManager
type TeamManagerService struct {
RandomStringGenerator func(length int) string
}
// in this way you don't need to change your main/where this code is used
func NewTeamManagerService() *TeamManagerService {
return &TeamManagerService{RandomStringGenerator: base36.GenerateRandomString}
}
func (m *TeamManagerService) CreateTeam(ctx context.Context) {
// we are using the struct field variable
code = m.RandomStringGenerator(5)
// your application logic
return nil
}
and in your test, you can use your own custom function
myGenerator = func(length int) string {
return "some string"
}
service := &teamManager.TeamManagerService{RandomStringGenerator: myGenerator}
service.CreateTeam(context.Background())
you are using testify like me :D you can do this
// this is the mock version of the base36 file
package base36_mock
import "github.com/stretchr/testify/mock"
var Mock = mock.Mock{}
func GenerateRandomString(length int) string {
args := Mock.Called(length)
return args.String(0)
}
and in your test, you can use your own custom function
base36_mock.Mock.On("GenerateRandomString", 5).Return("my expmle code for this test").Once()
service := &teamManager.TeamManagerService{RandomStringGenerator: base36_mock.GenerateRandomString}
service.CreateTeam(context.Background())
Warning: This might inflate executable file size a little bit and cost a little runtime performance. IMO, this would be better if golang has such feature like macro or function decorator.
If you want to mock functions without changing its API, the easiest way is to change the implementation a little bit:
func getPage(url string) string {
if GetPageMock != nil {
return GetPageMock()
}
// getPage real implementation goes here!
}
func downloader() {
if GetPageMock != nil {
return GetPageMock()
}
// getPage real implementation goes here!
}
var GetPageMock func(url string) string = nil
var DownloaderMock func() = nil
This way we can actually mock one function out of the others. For more convenient we can provide such mocking boilerplate:
// download.go
func getPage(url string) string {
if m.GetPageMock != nil {
return m.GetPageMock()
}
// getPage real implementation goes here!
}
func downloader() {
if m.GetPageMock != nil {
return m.GetPageMock()
}
// getPage real implementation goes here!
}
type MockHandler struct {
GetPage func(url string) string
Downloader func()
}
var m *MockHandler = new(MockHandler)
func Mock(handler *MockHandler) {
m = handler
}
In test file:
// download_test.go
func GetPageMock(url string) string {
// ...
}
func TestDownloader(t *testing.T) {
Mock(&MockHandler{
GetPage: GetPageMock,
})
// Test implementation goes here!
Mock(new(MockHandler)) // Reset mocked functions
}
I have been in similar spot. I was trying to write unitTest for a function which had numerous clients calling it. let me propose 2 options that I explored. one of which is already discussed in this thread, I will regardless repeat it for the sake of people searching.
Method 1: Declaring function you wanna mock as a Global variable
one option is declaring a global variable (has some pit falls).
eg:
package abc
var getFunction func(s string) (string, error) := http.Get
func get_page(url string) string {
....
resp, err := getFunction(url)
....
}
func downloader() {
.....
}
and the test func will be as follows:
package abc
func testFunction(t *testing.T) {
actualFunction := getFunction
getFunction := func(s string) (string, error) {
//mock implementation
}
defer getFunction = actualFunction
.....
//your test
......
}
NOTE: test and actual implementation are in the same package.
there are some restrictions with above method thought!
running parallel tests is not possible due to risk of race conditions.
by making function a variable, we are inducing a small risk of reference getting modified by future developers working in same package.
Method 2: Creating a wrapped function
another method is to pass along the methods you want to mock as arguments to the function to enable testability. In my case, I already had numerous clients calling this method and thus, I wanted to avoid violating the existing contracts. so, I ended up creating a wrapped function.
eg:
package abc
type getOperation func(s string) (string, error)
func get_page(url string, op getOperation) string {
....
resp, err := op(url)
....
}
//contains only 2 lines of code
func downloader(get httpGet) {
op := http.Get
content := wrappedDownloader(get, op)
}
//wraps all the logic that was initially in downloader()
func wrappedDownloader(get httpGet, op getOperation) {
....
content := get_page(BASE_URL, op)
....
}
now for testing the actual logic, you will test calls to wrappedDownloader instead of Downloader and you would pass it a mocked getOperation. this is allow you to test all the business logic while not violating your API contract with current clients of the method.
Considering unit test is the domain of this question, highly recommend you to use monkey. This Package make you to mock test without changing your original source code. Compare to other answer, it's more "non-intrusive".
main
type AA struct {
//...
}
func (a *AA) OriginalFunc() {
//...
}
mock test
var a *AA
func NewFunc(a *AA) {
//...
}
monkey.PatchMethod(reflect.TypeOf(a), "OriginalFunc", NewFunc)
Bad side is:
Reminded by Dave.C, This method is unsafe. So don't use it outside of unit test.
Is non-idiomatic Go.
Good side is:
Is non-intrusive. Make you do things without changing the main code. Like Thomas said.
Make you change behavior of package (maybe provided by third party) with least code.