Adding a new post on golang unit tests
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OLUWADAMILOLA OKUSANYA
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Title: Adventures in Golang (Tests)
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Date: 2023-11-27 22:04
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Category: Golang
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Tags: Things I learned
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Slug: golangtests
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Authors: Okusanya David
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Summary: About adding tests to a golang project
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### OUTLINE
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- [Problem statement](#golang-registry-tests-problem)
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- [First Approach](#golang-registry-tests-approach-one)
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- [Second Approach](#golang-registry-tests-approach-two)
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### PROBLEM STATEMENT {#golang-registry-tests-problem}
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So I had finished the first version of my code implementing a npm registry server in Go. This version has no tests. I have been testing it manually. I wanted to add filesystem locking and deploy the code through CI. So I needed to add automated tests(unit and integration) as I wanted complement my manual testing.
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Here is a snippet of what I wanted to write a unit test for:
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```golang
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package handler
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import (
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"fmt"
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"net/http"
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"net/url"
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"github.com/gorilla/mux"
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"github.com/sirupsen/logrus"
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"gosimplenpm/internal/config"
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"gosimplenpm/internal/storage"
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)
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func GetPackage(lg *logrus.Logger, cfg config.Config) http.HandlerFunc {
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return func(w http.ResponseWriter, r *http.Request) {
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escapedName := mux.Vars(r)["name"]
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packageName, _ := url.PathUnescape(escapedName)
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lg.WithFields(logrus.Fields{
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"function": "get-package",
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}).Debugf("Package name => %s\n", packageName)
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fileToServe, found, err := storage.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
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if err != nil {
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http.Error(w, err.Error(), http.StatusInternalServerError)
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return
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}
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if !found {
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ret := fmt.Sprintf("Package not found: %s", packageName)
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http.Error(w, ret, http.StatusNotFound)
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return
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}
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// serve file
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http.ServeFile(w, r, fileToServe)
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}
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}
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```
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So I wanted to test this function without also testing the `storage.GetIndexJsonFromStore` function. The `storage.GetIndexJsonFromStore` function makes calls to the filesystem. Well, coming from Javascript, I would use a mocking framework like Sinon.JS [^1] to mock out the `storage.GetIndexJsonFromStore` function without modifying the `GetPackage` handler.
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### FIRST APPROACH {#golang-registry-tests-approach-one}
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So using my limited knowledge of Go, I wrote an interface `Storage` and defined the method `GetIndexJsonFromStore` like below:
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```golang
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package storage
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import (
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"gosimplenpm/internal/serviceidos"
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"github.com/sirupsen/logrus"
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)
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type Storage interface {
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GetIndexJsonFromStore(string, string, *logrus.Logger) (string, bool, error)
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// Other methods omitted for brevity
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}
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```
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Then I can define a struct `MockFS` that would implement the method `GetIndexJsonFromStore`. This is because structs that implement all the methods of an interface are _objects_ of that interface.
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```golang
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type MockFs struct {
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packageJson string
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retrieved bool
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err error
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called bool
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}
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func (m *MockFs) SetError(err error) {
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m.err = err
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}
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func (m *MockFs) SetRetrieved(retrieved bool) {
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m.retrieved = retrieved
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}
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func (m *MockFs) SetFileToServe(fileToServe string) {
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m.packageJson = fileToServe
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}
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func (m *MockFs) GetIndexJsonFromStore(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
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m.called = true
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return m.packageJson, m.retrieved, m.err
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}
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```
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I would then modify the previously defined `GetIndexJsonFromStore` method to allow for me to inject the `MockFs` dependency.
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```golang
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package handler
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import (
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"fmt"
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"net/http"
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"net/url"
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"github.com/gorilla/mux"
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"github.com/sirupsen/logrus"
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"gosimplenpm/internal/config"
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"gosimplenpm/internal/storage"
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)
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func GetPackage(lg *logrus.Logger, cfg config.Config, stg storage.Storage) http.HandlerFunc {
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return func(w http.ResponseWriter, r *http.Request) {
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escapedName := mux.Vars(r)["name"]
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packageName, _ := url.PathUnescape(escapedName)
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lg.WithFields(logrus.Fields{
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"function": "get-package",
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}).Debugf("Package name => %s\n", packageName)
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fileToServe, found, err := stg.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
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if err != nil {
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http.Error(w, err.Error(), http.StatusInternalServerError)
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return
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}
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if !found {
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ret := fmt.Sprintf("Package not found: %s", packageName)
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http.Error(w, ret, http.StatusNotFound)
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return
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}
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// serve file
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http.ServeFile(w, r, fileToServe)
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}
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}
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```
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A sample test would be something like this
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```golang
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package handler
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import (
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"bytes"
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"fmt"
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"gosimplenpm/internal/config"
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"gosimplenpm/internal/storage"
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"io"
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"net/http"
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"net/http/httptest"
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"os"
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"testing"
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"github.com/gorilla/mux"
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"github.com/sirupsen/logrus"
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"github.com/stretchr/testify/assert"
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)
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func TestGet(t *testing.T) {
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t.Run("return `Not Found` error if package is not found", func(t *testing.T) {
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req := httptest.NewRequest(http.MethodGet, "/{name}", nil)
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wrt := httptest.NewRecorder()
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log := &logrus.Logger{
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Out: os.Stdout,
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Formatter: &logrus.TextFormatter{
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FullTimestamp: true,
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TimestampFormat: "2009-01-02 15:15:15",
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},
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}
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cfg := config.Config{
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RepoDir: "",
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}
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mfs := &storage.MockFs{}
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mfs.SetRetrieved(false)
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//Hack to try to fake gorilla/mux vars
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vars := map[string]string{
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"name": "test-package",
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}
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req = mux.SetURLVars(req, vars)
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GetPackage(log, cfg, mfs)(wrt, req)
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rs := wrt.Result()
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assert.Equal(t, rs.StatusCode, http.StatusNotFound)
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defer rs.Body.Close()
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body, err := io.ReadAll(rs.Body)
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if err != nil {
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t.Fatal(err)
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}
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bytes.TrimSpace(body)
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assert.Equal(t, string(body), "Package not found: test-package\n")
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})
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}
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```
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This approach fails if I wanted to test another function `stg.GetOtherJsonFromNet` of the interface like below:
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```golang
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package handler
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import (
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"fmt"
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"net/http"
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"net/url"
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"github.com/gorilla/mux"
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"github.com/sirupsen/logrus"
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"gosimplenpm/internal/config"
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"gosimplenpm/internal/storage"
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)
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func GetPackage(lg *logrus.Logger, cfg config.Config, stg storage.Storage) http.HandlerFunc {
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return func(w http.ResponseWriter, r *http.Request) {
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escapedName := mux.Vars(r)["name"]
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packageName, _ := url.PathUnescape(escapedName)
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lg.WithFields(logrus.Fields{
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"function": "get-package",
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}).Debugf("Package name => %s\n", packageName)
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fileToServe, found, err := stg.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
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if err != nil {
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http.Error(w, err.Error(), http.StatusInternalServerError)
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return
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}
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if !found {
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fileToServe, err = stg.GetOtherJsonFromNet(packageName, lg)
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if err != nil {
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http.Error(w, err.Error(), http.StatusInternalServerError)
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return
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}
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}
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//...code omitted for brevity
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}
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}
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```
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### SECOND APPROACH {#golang-registry-tests-approach-two}
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To handle this new scenario, that is, to test the other function `GetOtherJsonFromNet` as well as `GetIndexJsonFromStore`, I would modify the struct and its implementations to something like this:
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```golang
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type MockFs struct {
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GetIndexJsonFromStoreFunc func(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error)
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GetOtherJsonFromNetFunc func(packageName string, lg *logrus.Logger) (string, error)
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}
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func (m *MockFs) GetIndexJsonFromStore(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
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return m.GetIndexJsonFromStoreFunc(packageName, registryPath, lg)
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}
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func (m *MockFs) GetOtherJsonFromNet(packageName string, lg *logrus.Logger) (string, error) {
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return m.GetOtherJsonFromNetFunc(packageName, lg)
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}
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```
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Basically since I cannot reassign a function to an already defined struct (as I could in Javascript with objects), I would instead define function variables as part of the `MockFS` struct. That way, I can redefine those function variables for each test I want to run. An example of a test that uses this is shown below:
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```golang
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package handler
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import (
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"bytes"
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"fmt"
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"gosimplenpm/internal/config"
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"gosimplenpm/internal/storage"
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"io"
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"net/http"
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"net/http/httptest"
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"os"
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"testing"
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"github.com/gorilla/mux"
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"github.com/sirupsen/logrus"
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"github.com/stretchr/testify/assert"
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)
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func TestGet(t *testing.T) {
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t.Run("return `Internal Server` error if package cannot be retrieved either from disk or from the internet", func(t *testing.T) {
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req := httptest.NewRequest(http.MethodGet, "/{name}", nil)
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wrt := httptest.NewRecorder()
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log := &logrus.Logger{
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Out: os.Stdout,
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Formatter: &logrus.TextFormatter{
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FullTimestamp: true,
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TimestampFormat: "2009-01-02 15:15:15",
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},
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}
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cfg := config.Config{
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RepoDir: "",
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}
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mfs := &storage.MockFs{}
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mfs.GetIndexJsonFromStore = func (packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
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return "", false, fmt.Errorf("Failure to retrieve disk")
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}
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mfs.GetOtherJsonFromNet = func (packageName string, lg *logrus.Logger) (string, error) {
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return "", false, fmt.Errorf("Failure to retrieve from internet")
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}
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//Hack to try to fake gorilla/mux vars
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vars := map[string]string{
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"name": "test-package",
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}
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req = mux.SetURLVars(req, vars)
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GetPackage(log, cfg, mfs)(wrt, req)
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rs := wrt.Result()
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assert.Equal(t, rs.StatusCode, http.StatusInternalServerErro)
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defer rs.Body.Close()
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body, err := io.ReadAll(rs.Body)
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if err != nil {
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t.Fatal(err)
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}
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bytes.TrimSpace(body)
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assert.Equal(t, string(body), "Failure to retrieve from internet\n")
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})
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}
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```
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This approach avoids the usage of struct-level variables, making it easier to easily fine-tune your tests.
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Now, I had already moved all my tests to this approach before I found out about GoMock[^2]. In the future, I may move to GoMock[^2] instead.
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[^1]: [Sinon.JS](https://sinonjs.org/)
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[^2]: [GoMock](https://github.com/golang/mock)
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