How can I unit test Google App Engine Go HTTP handlers?

Question

Local unit testing is supported from version 1.8.6 of the Google App Engine Go SDK. The appengine/aetest package allows me to create a Context to unit test with.

How can I use this with net/http/httptest to test my HTTP handlers?

Answer 1

See the top of goroot/src/pkg/appengine/aetest/context.go (updated source is not yet posted at https://code.google.com/p/appengine-go). At first glance, the new testing app looks to be a slightly beefier/different version of appenginetesting so you can do the same sorts of tests, see here for one way to do it with how sampleHandler(w http.ResponseWriter, r *http.Request) is called.

Alternatively, you can make your http.Handler's ContextHandler like as below:

type ContextHandler struct {
    Real func(*appengine.Context, http.ResponseWriter, *http.Request)
}

func (f ContextHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    c := appengine.NewContext(r)
    f.Real(c, w, r)
}

func myNewHandler(c appengine.Context, w http.ResponseWriter, r *http.Request) {
// do something
}

Then you can do this in init() to support production:

http.Handle("/myNewHandler", ContextHandler{myNewHandler})

This makes testing the function easy:

func TestMyNewHandler(t *testing.T) {
    c := aetest.NewContext()
    r, _ := http.NewRequest("GET", "/tasks/findOverdueSchedules", nil)
    w := httptest.NewRecorder()
    myNewHandler(c, w, r)
    if 200 != w.Code {
        t.Fail()
    }
}

Here's what's from context.go inside appengine/aetest:

/* Package aetest provides an appengine.Context for use in tests.

An example test file: package foo_test

import (
    "testing"

    "appengine/memcache"
    "appengine/aetest"
)

func TestFoo(t *testing.T) {
    c, err := aetest.NewContext(nil)
    if err != nil {
        t.Fatal(err)
    }
    defer c.Close()

    it := &memcache.Item{
        Key:   "some-key",
        Value: []byte("some-value"),
    }
    err = memcache.Set(c, it)
    if err != nil {
        t.Fatalf("Set err: %v", err)
    }
    it, err = memcache.Get(c, "some-key")
    if err != nil {
        t.Fatalf("Get err: %v; want no error", err)
    }
    if g, w := string(it.Value), "some-value" ; g != w {
        t.Errorf("retrieved Item.Value = %q, want %q", g, w)
    }
}

The environment variable APPENGINE_API_SERVER specifies the location of the api_server.py executable to use. If unset, the system PATH is consulted. */