Adventures in Golang (Tests)
OUTLINE
PROBLEM STATEMENT
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.
Here is a snippet of what I wanted to write a unit test for:
package handler
import (
"fmt"
"net/http"
"net/url"
"github.com/gorilla/mux"
"github.com/sirupsen/logrus"
"gosimplenpm/internal/config"
"gosimplenpm/internal/storage"
)
func GetPackage(lg *logrus.Logger, cfg config.Config) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
escapedName := mux.Vars(r)["name"]
packageName, _ := url.PathUnescape(escapedName)
lg.WithFields(logrus.Fields{
"function": "get-package",
}).Debugf("Package name => %s\n", packageName)
fileToServe, found, err := storage.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
if !found {
ret := fmt.Sprintf("Package not found: %s", packageName)
http.Error(w, ret, http.StatusNotFound)
return
}
// serve file
http.ServeFile(w, r, fileToServe)
}
}
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.
FIRST APPROACH
So using my limited knowledge of Go, I wrote an interface Storage and defined the method GetIndexJsonFromStore like below:
package storage
import (
"gosimplenpm/internal/serviceidos"
"github.com/sirupsen/logrus"
)
type Storage interface {
GetIndexJsonFromStore(string, string, *logrus.Logger) (string, bool, error)
// Other methods omitted for brevity
}
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.
type MockFs struct {
packageJson string
retrieved bool
err error
called bool
}
func (m *MockFs) SetError(err error) {
m.err = err
}
func (m *MockFs) SetRetrieved(retrieved bool) {
m.retrieved = retrieved
}
func (m *MockFs) SetFileToServe(fileToServe string) {
m.packageJson = fileToServe
}
func (m *MockFs) GetIndexJsonFromStore(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
m.called = true
return m.packageJson, m.retrieved, m.err
}
I would then modify the previously defined GetIndexJsonFromStore method to allow for me to inject the MockFs dependency.
package handler
import (
"fmt"
"net/http"
"net/url"
"github.com/gorilla/mux"
"github.com/sirupsen/logrus"
"gosimplenpm/internal/config"
"gosimplenpm/internal/storage"
)
func GetPackage(lg *logrus.Logger, cfg config.Config, stg storage.Storage) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
escapedName := mux.Vars(r)["name"]
packageName, _ := url.PathUnescape(escapedName)
lg.WithFields(logrus.Fields{
"function": "get-package",
}).Debugf("Package name => %s\n", packageName)
fileToServe, found, err := stg.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
if !found {
ret := fmt.Sprintf("Package not found: %s", packageName)
http.Error(w, ret, http.StatusNotFound)
return
}
// serve file
http.ServeFile(w, r, fileToServe)
}
}
A sample test would be something like this
package handler
import (
"bytes"
"fmt"
"gosimplenpm/internal/config"
"gosimplenpm/internal/storage"
"io"
"net/http"
"net/http/httptest"
"os"
"testing"
"github.com/gorilla/mux"
"github.com/sirupsen/logrus"
"github.com/stretchr/testify/assert"
)
func TestGet(t *testing.T) {
t.Run("return `Not Found` error if package is not found", func(t *testing.T) {
req := httptest.NewRequest(http.MethodGet, "/{name}", nil)
wrt := httptest.NewRecorder()
log := &logrus.Logger{
Out: os.Stdout,
Formatter: &logrus.TextFormatter{
FullTimestamp: true,
TimestampFormat: "2009-01-02 15:15:15",
},
}
cfg := config.Config{
RepoDir: "",
}
mfs := &storage.MockFs{}
mfs.SetRetrieved(false)
//Hack to try to fake gorilla/mux vars
vars := map[string]string{
"name": "test-package",
}
req = mux.SetURLVars(req, vars)
GetPackage(log, cfg, mfs)(wrt, req)
rs := wrt.Result()
assert.Equal(t, rs.StatusCode, http.StatusNotFound)
defer rs.Body.Close()
body, err := io.ReadAll(rs.Body)
if err != nil {
t.Fatal(err)
}
bytes.TrimSpace(body)
assert.Equal(t, string(body), "Package not found: test-package\n")
})
}
This approach fails if I wanted to test another function stg.GetOtherJsonFromNet of the interface like below:
package handler
import (
"fmt"
"net/http"
"net/url"
"github.com/gorilla/mux"
"github.com/sirupsen/logrus"
"gosimplenpm/internal/config"
"gosimplenpm/internal/storage"
)
func GetPackage(lg *logrus.Logger, cfg config.Config, stg storage.Storage) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
escapedName := mux.Vars(r)["name"]
packageName, _ := url.PathUnescape(escapedName)
lg.WithFields(logrus.Fields{
"function": "get-package",
}).Debugf("Package name => %s\n", packageName)
fileToServe, found, err := stg.GetIndexJsonFromStore(packageName, cfg.RepoDir, lg)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
if !found {
fileToServe, err = stg.GetOtherJsonFromNet(packageName, lg)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
}
//...code omitted for brevity
}
}
SECOND APPROACH
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:
type MockFs struct {
GetIndexJsonFromStoreFunc func(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error)
GetOtherJsonFromNetFunc func(packageName string, lg *logrus.Logger) (string, error)
}
func (m *MockFs) GetIndexJsonFromStore(packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
return m.GetIndexJsonFromStoreFunc(packageName, registryPath, lg)
}
func (m *MockFs) GetOtherJsonFromNet(packageName string, lg *logrus.Logger) (string, error) {
return m.GetOtherJsonFromNetFunc(packageName, lg)
}
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:
package handler
import (
"bytes"
"fmt"
"gosimplenpm/internal/config"
"gosimplenpm/internal/storage"
"io"
"net/http"
"net/http/httptest"
"os"
"testing"
"github.com/gorilla/mux"
"github.com/sirupsen/logrus"
"github.com/stretchr/testify/assert"
)
func TestGet(t *testing.T) {
t.Run("return `Internal Server` error if package cannot be retrieved either from disk or from the internet", func(t *testing.T) {
req := httptest.NewRequest(http.MethodGet, "/{name}", nil)
wrt := httptest.NewRecorder()
log := &logrus.Logger{
Out: os.Stdout,
Formatter: &logrus.TextFormatter{
FullTimestamp: true,
TimestampFormat: "2009-01-02 15:15:15",
},
}
cfg := config.Config{
RepoDir: "",
}
mfs := &storage.MockFs{}
mfs.GetIndexJsonFromStore = func (packageName string, registryPath string, lg *logrus.Logger) (string, bool, error) {
return "", false, fmt.Errorf("Failure to retrieve disk")
}
mfs.GetOtherJsonFromNet = func (packageName string, lg *logrus.Logger) (string, error) {
return "", false, fmt.Errorf("Failure to retrieve from internet")
}
//Hack to try to fake gorilla/mux vars
vars := map[string]string{
"name": "test-package",
}
req = mux.SetURLVars(req, vars)
GetPackage(log, cfg, mfs)(wrt, req)
rs := wrt.Result()
assert.Equal(t, rs.StatusCode, http.StatusInternalServerErro)
defer rs.Body.Close()
body, err := io.ReadAll(rs.Body)
if err != nil {
t.Fatal(err)
}
bytes.TrimSpace(body)
assert.Equal(t, string(body), "Failure to retrieve from internet\n")
})
}
This approach avoids the usage of struct-level variables, making it easier to easily fine-tune your tests.
Now, I had already moved all my tests to this approach before I found out about GoMock2. In the future, I may move to GoMock2 instead.