Make mock gin.Context in Golang - unit-testing

Question

I'm writing a REST API using Gin framework. But I was faced a trouble testing my controllers and researching TDD and Mock. I tried to apply TDD and Mock to my code but I could not.
I created a very reduced test environment and tried to create a controller test. How do I create a Mock for Gin.Context?
Here's my example code:
package main
import (
"strconv"
"github.com/gin-gonic/gin"
)
// MODELS
type Users []User
type User struct {
Name string `json"name"`
}
func main() {
r := gin.Default()
r.GET("/users", GetUsers)
r.GET("/users/:id", GetUser)
r.Run(":8080")
}
// ROUTES
func GetUsers(c *gin.Context) {
repo := UserRepository{}
ctrl := UserController{}
ctrl.GetAll(c, repo)
}
func GetUser(c *gin.Context) {
repo := UserRepository{}
ctrl := UserController{}
ctrl.Get(c, repo)
}
// CONTROLLER
type UserController struct{}
func (ctrl UserController) GetAll(c *gin.Context, repository UserRepositoryIterface) {
c.JSON(200, repository.GetAll())
}
func (ctrl UserController) Get(c *gin.Context, repository UserRepositoryIterface) {
id := c.Param("id")
idConv, _ := strconv.Atoi(id)
c.JSON(200, repository.Get(idConv))
}
// REPOSITORY
type UserRepository struct{}
type UserRepositoryIterface interface {
GetAll() Users
Get(id int) User
}
func (r UserRepository) GetAll() Users {
users := Users{
{Name : "Wilson"},
{Name : "Panda"},
}
return users
}
func (r UserRepository) Get(id int) User {
users := Users{
{Name : "Wilson"},
{Name : "Panda"},
}
return users[id-1]
}
My test example:
package main
import(
"testing"
_ "github.com/gin-gonic/gin"
)
type UserRepositoryMock struct{}
func (r UserRepositoryMock) GetAll() Users {
users := Users{
{Name : "Wilson"},
{Name : "Panda"},
}
return users
}
func (r UserRepositoryMock) Get(id int) User {
users := Users{
{Name : "Wilson"},
{Name : "Panda"},
}
return users[id-1]
}
// TESTING REPOSITORY FUNCTIONS
func TestRepoGetAll(t *testing.T) {
userRepo := UserRepository{}
amountUsers := len(userRepo.GetAll())
if amountUsers != 2 {
t.Errorf("Esperado %d, recebido %d", 2, amountUsers)
}
}
func TestRepoGet(t *testing.T) {
expectedUser := struct{
Name string
}{
"Wilson",
}
userRepo := UserRepository{}
user := userRepo.Get(1)
if user.Name != expectedUser.Name {
t.Errorf("Esperado %s, recebido %s", expectedUser.Name, user.Name)
}
}
/* HOW TO TEST CONTROLLER?
func TestControllerGetAll(t *testing.T) {
gin.SetMode(gin.TestMode)
c := &gin.Context{}
c.Status(200)
repo := UserRepositoryMock{}
ctrl := UserController{}
ctrl.GetAll(c, repo)
}
*/

Answer 1

Gin provides the option to create a Test Context which you can use for whatever you need:
https://godoc.org/github.com/gin-gonic/gin#CreateTestContext
Like that:
c, _ := gin.CreateTestContext(httptest.NewRecorder())

Answer 2

Here is an example of how I mock a context, add a param, use it in a function, then print the string of the response if there was a non-200 response.
gin.SetMode(gin.TestMode)
w := httptest.NewRecorder()
c, _ := gin.CreateTestContext(w)
c.Params = []gin.Param{gin.Param{Key: "k", Value: "v"}}
foo(c)
if w.Code != 200 {
b, _ := ioutil.ReadAll(w.Body)
t.Error(w.Code, string(b))
}

Answer 3

In order to get a *gin.Context instance that you can test, you need a mock HTTP request and response. An easy way to create those is to use the net/http and net/http/httptest packages. Based on the code you linked, your test would look like this:
package main
import (
"net/http"
"net/http/httptest"
"testing"
"github.com/gin-gonic/gin"
)
func TestControllerGetAll(t *testing.T) {
// Switch to test mode so you don't get such noisy output
gin.SetMode(gin.TestMode)
// Setup your router, just like you did in your main function, and
// register your routes
r := gin.Default()
r.GET("/users", GetUsers)
// Create the mock request you'd like to test. Make sure the second argument
// here is the same as one of the routes you defined in the router setup
// block!
req, err := http.NewRequest(http.MethodGet, "/users", nil)
if err != nil {
t.Fatalf("Couldn't create request: %v\n", err)
}
// Create a response recorder so you can inspect the response
w := httptest.NewRecorder()
// Perform the request
r.ServeHTTP(w, req)
// Check to see if the response was what you expected
if w.Code != http.StatusOK {
t.Fatalf("Expected to get status %d but instead got %d\n", http.StatusOK, w.Code)
}
}
Although you could create a mock *gin.Context, it's probably easier to use the method above, since it'll execute and handle your request the same as it would an actual request.

Answer 4

If to reduce the question to "How to create mock for a function argument?" the answer is: use interfaces not concrete types.
type Context struct is a concrete type literal and Gin doesn't provide appropriate interface. But you can declare it by yourself. Since you are using only JSON method from Context you can declare extra-simple interface:
type JSONer interface {
JSON(code int, obj interface{})
}
And use JSONer type instead Context type in all your functions which expect Context as argument:
/* Note, you can't declare argument as a pointer to interface type,
but when you call it you can pass pointer to type which
implements the interface.*/
func GetUsers(c JSONer) {
repo := UserRepository{}
ctrl := UserController{}
ctrl.GetAll(c, repo)
}
func GetUser(c JSONer) {
repo := UserRepository{}
ctrl := UserController{}
ctrl.Get(c, repo)
}
func (ctrl UserController) GetAll(c JSONer, repository UserRepositoryIterface) {
c.JSON(200, repository.GetAll())
}
func (ctrl UserController) Get(c JSONer, repository UserRepositoryIterface) {
id := c.Param("id")
idConv, _ := strconv.Atoi(id)
c.JSON(200, repository.Get(idConv))
}
And now it is easy to test
type ContextMock struct {
JSONCalled bool
}
func (c *ContextMock) JSON(code int, obj interface{}){
c.JSONCalled = true
}
func TestControllerGetAll(t *testing.T) {
gin.SetMode(gin.TestMode)
c := &ContextMock{false}
c.Status(200)
repo := UserRepositoryMock{}
ctrl := UserController{}
ctrl.GetAll(c, repo)
if c.JSONCalled == false {
t.Fail()
}
}
Example simple as possible.
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