Testing HTTP handlers in Go

Introduction

In this example, I will create unit tests using the httptest library and we will see how to create test coverage for http handlers.

How to test http handlers in Go?

So we can test any handler http, we need a structure to be able to store the handler response, such as http status code, headers, body, etc.
The package httptest provide the structure httptest.ResponseRecorder, that's all we need to store the handler response.

// NewRecorder returns an initialized ResponseRecorder.
func NewRecorder() *ResponseRecorder {
    return &ResponseRecorder{
        HeaderMap: make(http.Header),
        Body:      new(bytes.Buffer),
        Code:      200,
    }
}

The sample API

In our sample API, we have a handler called /check-is-prime, which checks if a number is prime.

The code:

The first test

The logic of the tests is very simple, for each test we build the HTTP request and then compare the response.

Adding more tests

Using table design in tests, its easy to add more cases:

{
    name: "must return http.StatusOk and true to prime number (7)",
    args: func(*testing.T) args {
        req, err := http.NewRequest("GET", "/check-is-prime", nil)
        if err != nil {
            t.Fatalf("fail to create request: %s", err.Error())
        }

        q := req.URL.Query()
        q.Add("number", "7")
        req.URL.RawQuery = q.Encode()

        return args{
            req: req,
        }
    },
    wantCode: http.StatusOK,
    wantBody: "true",
},
{
    name: "must return http.StatusOk and false because number (1) is not prime",
    args: func(*testing.T) args {
        req, err := http.NewRequest("GET", "/check-is-prime", nil)
        if err != nil {
            t.Fatalf("fail to create request: %s", err.Error())
        }

        q := req.URL.Query()
        q.Add("number", "1")
        req.URL.RawQuery = q.Encode()

        return args{
            req: req,
        }
    },
    wantCode: http.StatusOK,
    wantBody: "false",
},