Test API endpoints with AWS SDK integration

[LorenRd]

I'm trying to test my API endpoint that list files from an AWS S3 Bucket:

func listFiles(w http.ResponseWriter, _ *http.Request) {
    client := GetAWSClient()
    bucket := aws.String(BUCKETNAME)

    input := &s3.ListObjectsV2Input{
        Bucket: bucket,
    }

    resp, err := GetObjects(context.TODO(), client, input)
    if err != nil {
        ...
    }

    msg, _ := json.Marshal(resp.Contents)
    w.WriteHeader(200)
    w.Write(msg)
    return
}
...

func handleRequest() {
	myRouter := mux.NewRouter().StrictSlash(true)
	myRouter.HandleFunc("/listFiles", listFiles).Methods("GET")
	c := cors.Default()
	handler := c.Handler(myRouter)
	log.Fatal(http.ListenAndServe(":8080", handler))
}

I see from AWS SDK documentation that to mock AWS client functions you can use it interface so in my main_test.go I created these:

//Testing /listFiles endpoint

type mockListObjectsAPI func(ctx context.Context, params *s3.ListObjectsV2Input, optFns ...func(*s3.Options)) (*s3.ListObjectsV2Output, error)

func (m mockListObjectsAPI) ListObjectsV2(ctx context.Context, params *s3.ListObjectsV2Input, optFns ...func(*s3.Options)) (*s3.ListObjectsV2Output, error) {
	return m(ctx, params, optFns...)
}

func TestGetObjectFromS3(t *testing.T) {
	cases := []struct {
		client func(t *testing.T) S3ListObjectsAPI
		bucket string
		key    string
		expect []byte
	}{
		{
			client: func(t *testing.T) S3ListObjectsAPI {
				return mockListObjectsAPI(func(ctx context.Context, params *s3.ListObjectsV2Input, optFns ...func(*s3.Options)) (*s3.ListObjectsV2Output, error) {
					t.Helper()
					if params.Bucket == nil {
						t.Fatal("expect bucket to not be nil")
					}
					if e, a := "fooBucket", *params.Bucket; e != a {
						t.Errorf("expect %v, got %v", e, a)
					}
					return &s3.ListObjectsV2Output{
						Name: aws.String("fooBucket"),
					}, nil
				})
			},
			bucket: "fooBucket",
			key:    "barKey",
			expect: []byte("this is the body foo bar baz"),
		},
		//Add more test cases here if needed
	}

	for i, tt := range cases {
		t.Run(strconv.Itoa(i), func(t *testing.T) {
           //Here I should compare API returned value with expected in the test cases
		})
	}
}

My question is, how could I test my API calling it from the test but without calling AWS but instead using the values I mocked?

If I use httptest to call the endpoint it will call the real endpoint calling AWS.