Golang Testing HTTP Handler

FaFiFu

This section is a bullshittery, you can skip it to the main section

It's been a year since my last blog post, 2023 is quite a year that makes me hard to spend time updating this blog. The thing is, going back working from the office take hours of productive hour. Going to the office preparation, commuting, chit-chat, snack time makes me less productive. Nah, that's maybe the me issue, just trying to blame others because it's easier :D. Just hoping that I will have enough time to update this blog more frequent in 2024. Enough of the chit-chat, let's go to the main section.

Introduction

When you start working with Golang as a web server and developing some HTTP endpoints, you might want to test it as well. In Golang, in order to test the HTTP endpoints, it has a specific library called httptest. I also have created one blog post that highlight one specific use case of httptest related to mocking external HTTP call, you can read it here.

Components

To create a unit test for testing HTTP endpoints, we can utilize httptest.NewRecorder and httptest.NewRequest. If you remember, golang basic http.Handler looks like below:

func FooHandler(w http.ResponseWriter, r *http.Request) {}

It needs both http.ResponseWriter and http.Request, which the value of both of them will be provided by http.Server whenever a new request is coming to the handler. In testing, instead of running an http.Server that will provide the value, you can fill the argument using httptest.NewRecorder and httptest.NewRequest functions return value since both of the function consecutively return http.ResponseWriter and http.Request.

Code

Now let's go to the code. Let's say you have this handler that you want to test:

package handler

import (
    "fmt"
    "net/http"
)

func RootHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "[%s] %s OK!", r.Method, r.URL.String())
}

It's quite a simple handler, let's create a test for RootHandler:

package handler_test

import (
    "fmt"
    "io"
    "net/http"
    "net/http/httptest"
    "testing"

    "github.com/clavinjune/example/handler"
)

func TestRootHandler(t *testing.T) {
    method := http.MethodPost
    endpoint := "/foo"

    w := httptest.NewRecorder()
    r := httptest.NewRequest(method, endpoint, http.NoBody)
    defer r.Body.Close()

    handler.RootHandler(w, r)
    defer w.Result().Body.Close()

    if w.Result().StatusCode != http.StatusOK {
        t.Fatalf("want: %03d, got: %03d", http.StatusOK, w.Result().StatusCode)
    }

    b, err := io.ReadAll(w.Result().Body)
    if err != nil {
        t.Fatalf("want: nil, got: %+q", err)
    }

    want := fmt.Sprintf(`[%s] %s OK!`, method, endpoint)
    got := string(b)

    if want != got {
        t.Fatalf("want: %+q, got: %+q", want, got)
    }
}

As you see the example above, we called handler.RootHandler(w, r) where the argument is filled by the httptest.NewRecorder and http.NewRequest. The recorder, will record whatever the response of the handler, you can read the body, status code, header, etc by only using w.Result(). Meanwhile the request will create a similar request like http.NewRequest with some hard-coded fields since httptest.NewRequest creates an incoming server request not like http.NewRequest that creates a client HTTP request which are usually used in http.Client{}.Do function, and that's it. Now you have the unit test for your HTTP handler.

Thank you for reading!