Mocking for unit-tests and e2e-tests in golang

• 02, 07, 2021
•  bullgare
•  golang, Testing
• No Comments.

Some patterns to test your golang app.

Mocking an interface

	mockS3 := &mocks.S3API{}

	mockResultFn := func(input *s3.ListObjectsInput) *s3.ListObjectsOutput {
		output := &s3.ListObjectsOutput{}
		output.SetCommonPrefixes([]*s3.CommonPrefix{
			&s3.CommonPrefix{
				Prefix: aws.String("2017-01-01"),
			},
		})
		return output
	}

	// NB: .Return(...) must return the same signature as the method being mocked.
	//     In this case it's (*s3.ListObjectsOutput, error).
	mockS3.On("ListObjects", mock.MatchedBy(func(input *s3.ListObjectsInput) bool {
		return input.Delimiter != nil && *input.Delimiter == "/" && input.Prefix == nil
	})).Return(mockResultFn, nil)

	listingInput := &s3.ListObjectsInput{
		Bucket:    aws.String("foo"),
		Delimiter: aws.String("/"),
	}
	listingOutput, err := mockS3.ListObjects(listingInput)
	if err != nil {
		panic(err)
	}

	for _, x := range listingOutput.CommonPrefixes {
		fmt.Printf("common prefix: %+v\n", *x)
	}

https://github.com/vektra/mockery

Mocking SQL database

// a successful case
func TestShouldUpdateStats(t *testing.T) {
	db, mock, err := sqlmock.New()
	if err != nil {
		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
	}
	defer db.Close()

	mock.ExpectBegin()
	mock.ExpectExec("UPDATE products").WillReturnResult(sqlmock.NewResult(1, 1))
	mock.ExpectExec("INSERT INTO product_viewers").WithArgs(2, 3).WillReturnResult(sqlmock.NewResult(1, 1))
	mock.ExpectCommit()

	// now we execute our method
	if err = recordStats(db, 2, 3); err != nil {
		t.Errorf("error was not expected while updating stats: %s", err)
	}

	// we make sure that all expectations were met
	if err := mock.ExpectationsWereMet(); err != nil {
		t.Errorf("there were unfulfilled expectations: %s", err)
	}
}

https://github.com/DATA-DOG/go-sqlmock

Mocking HTTP server for unit-tests

	handler := func(w http.ResponseWriter, r *http.Request) {
		io.WriteString(w, "Hello World!")
	}

	req := httptest.NewRequest("GET", "http://example.com/foo", nil)
	w := httptest.NewRecorder()
	handler(w, req)

	resp := w.Result()
	body, _ := ioutil.ReadAll(resp.Body)

	fmt.Println(resp.StatusCode)
	fmt.Println(resp.Header.Get("Content-Type"))
	fmt.Println(string(body))

https://golang.org/pkg/net/http/httptest/

Stubbing HTTP server for e2e-tests

{
	"host": "example.com",
	"method": "GET|POST|PUT|PATCH|... (Mandatory)", 
	"path": "/your/path/:variable (Mandatory)",
	"queryStringParameters": {
		"name": ["value"],
		"name": ["value", "value"]
	},
	"headers": {
		"name": ["value"]
	},
	"cookies": {
		"name": "value"
	},
	"body": "Expected Body"
}

https://github.com/jmartin82/mmock

Mocking for e2e-tests with dockertest

var db *sql.DB

func TestMain(m *testing.M) {
	// uses a sensible default on windows (tcp/http) and linux/osx (socket)
	pool, err := dockertest.NewPool("")
	if err != nil {
		log.Fatalf("Could not connect to docker: %s", err)
	}

	// pulls an image, creates a container based on it and runs it
	resource, err := pool.Run("mysql", "5.7", []string{"MYSQL_ROOT_PASSWORD=secret"})
	if err != nil {
		log.Fatalf("Could not start resource: %s", err)
	}

	// exponential backoff-retry, because the application in the container might not be ready to accept connections yet
	if err := pool.Retry(func() error {
		var err error
		db, err = sql.Open("mysql", fmt.Sprintf("root:secret@(localhost:%s)/mysql", resource.GetPort("3306/tcp")))
		if err != nil {
			return err
		}
		return db.Ping()
	}); err != nil {
		log.Fatalf("Could not connect to docker: %s", err)
	}

	code := m.Run()
	
	// You can't defer this because os.Exit doesn't care for defer
	if err := pool.Purge(resource); err != nil {
		log.Fatalf("Could not purge resource: %s", err)
	}
	
	os.Exit(code)
}

func TestSomething(t *testing.T) {
	// db.Query()
}

https://github.com/ory/dockertest