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Question

Trying to mock http response in Go test. The code snippet below never terminates if I run it with

go test example.com/auth/...

package auth_test
import (
    "testing"
    "net/http/httptest"
    "net/http"
)

func TestAuthorization(t *testing.T) {
    t.Log("Should return 401 when Gateway returns 401")
    {
        url := oneOffUrlWithResponseCode(http.StatusUnauthorized)
        request, _ := http.NewRequest("GET", url, nil)
        response, _ := http.DefaultClient.Do(request)

        if response.StatusCode != http.StatusUnauthorized {
            t.Fatalf("Response should be 401 (Unauthorized)")
        }
    }
}

func oneOffUrlWithResponseCode(responseCode int) string {
    var server *httptest.Server
    server = httptest.NewServer(http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
        defer server.Close()
        response.WriteHeader(responseCode)
    }))
    return server.URL
}

However, if I comment out this line

defer server.Close()

everything works fine.

Ideally, I do not want to "leak" *httptest.Server outside of oneOffUrlWithResponseCode function and obviously close it after first request.

Why it never terminates? What am I doing wrong? What is the right thing to do?

Answer 1

The program doesn't terminate because of a deadlock (and it has nothing to do with closures). You cannot call Close inside a handler because internally Close waits for all handlers to finish.

The easiest way to fix it is to "leak" httptest.Server outside of oneOffUrlWithResponseCode:

func TestAuthorization(t *testing.T) {
    ...
    server := oneOffUrlWithResponseCode(http.StatusUnauthorized)
    defer server.Close()
    request, _ := http.NewRequest("GET", server.URL, nil)
    ...
}

func oneOffUrlWithResponseCode(responseCode int) *httptest.Server {
    return httptest.NewServer(http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
        response.WriteHeader(responseCode)
    }))
}