我們用go開發一個Web Server後，打算單元測試寫的handler函式，在不知道httptest之前，使用比較笨的方法
就是編譯執行該Web Server後，再用go編寫一個客戶端程式向該Web Server對應的route傳送資料然後解析
返回的資料。這個方法測試時非常麻煩，使用httptest來測試的話就非常簡單，可以和testing測試一起使用。

httptest基本使用方法

假設在server中handler已經寫好

http.HandleFunc("/health-check", HealthCheckHandler)

func HealthCheckHandler(w http.ResponseWriter, r *http.Request) {
    // A very simple health check.
 

    w.WriteHeader(http.StatusOK)
    w.Header().Set("Content-Type", "application/json")

    // In the future we could report back on the status of our DB, or our cache 
    // (e.g. Redis) by performing a simple PING, and include them in the response.
    io.WriteString(w, `{"alive": true}`)
}

測試如下：

import (
    "net/http"
 

    "net/http/httptest"
    "testing"
)

func TestHealthCheckHandler(t *testing.T) {
    //建立一個請求
    req, err := http.NewRequest("GET", "/health-check", nil)
    if err != nil {
        t.Fatal(err)
    }

    // 我們建立一個 ResponseRecorder (which satisfies http.ResponseWriter)來記錄響應
    rr := httptest.NewRecorder
 
()

    //直接使用HealthCheckHandler，傳入引數rr,req
    HealthCheckHandler(rr, req)

    // 檢測返回的狀態碼
    if status := rr.Code; status != http.StatusOK {
        t.Errorf("handler returned wrong status code: got %v want %v",
            status, http.StatusOK)
    }

    // 檢測返回的資料
    expected := `{"alive": true}`
    if rr.Body.String() != expected {
        t.Errorf("handler returned unexpected body: got %v want %v",
            rr.Body.String(), expected)
    }
}

然後就可以使用run test來執行測試.

如果Web Server有操作資料庫的行為，需要在init函式中進行資料庫的連線。

參考官方文件中的樣例編寫的另外一個測試程式碼：

func TestHealthCheckHandler2(t *testing.T) {
    reqData := struct {
        Info string `json:"info"`
    }{Info: "P123451"}

    reqBody, _ := json.Marshal(reqData)
    fmt.Println("input:", string(reqBody))
    req := httptest.NewRequest(
        http.MethodPost,
        "/health-check",
        bytes.NewReader(reqBody),
    )

    req.Header.Set("userid", "wdt")
    req.Header.Set("commpay", "brk")

    rr := httptest.NewRecorder()
    HealthCheckHandler(rr, req)

    result := rr.Result()

    body, _ := ioutil.ReadAll(result.Body)
    fmt.Println(string(body))

    if result.StatusCode != http.StatusOK {
        t.Errorf("expected status 200,",result.StatusCode)
    }
}

注意不同的地方
- http.NewRequest替換為httptest.NewRequest。
- httptest.NewRequest的第三個引數可以用來傳遞body資料，必須實現io.Reader介面。
- httptest.NewRequest不會返回error，無需進行err!=nil檢查。
- 解析響應時沒直接使用ResponseRecorder，而是呼叫了Result函式。

結合context使用

func TestGetProjectsHandler(t *testing.T) {
    req, err := http.NewRequest("GET", "/api/users", nil)
    if err != nil {
        t.Fatal(err)
    }

    rr := httptest.NewRecorder()
    // e.g. func GetUsersHandler(ctx context.Context, w http.ResponseWriter, r *http.Request)
    handler := http.HandlerFunc(GetUsersHandler)

    // Populate the request's context with our test data.
    ctx := req.Context()
    ctx = context.WithValue(ctx, "app.auth.token", "abc123")
    ctx = context.WithValue(ctx, "app.user",
        &YourUser{ID: "qejqjq", Email: "[email protected]"})

    // Add our context to the request: note that WithContext returns a copy of
    // the request, which we must assign.
    req = req.WithContext(ctx)
    handler.ServeHTTP(rr, req)

    // Check the status code is what we expect.
    if status := rr.Code; status != http.StatusOK {
        t.Errorf("handler returned wrong status code: got %v want %v",
            status, http.StatusOK)
    }
}

參考

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