in category Golang
Extracting the business logic - the project
In the last article, we wrote a few tests for a project to make sure that our refactoring won’t break anything. To understand the project better, we will separate the part of the domain and add a test to it. This will make the test more authentic.
There is a problem with the end-to-end (e2e) tests: database under the hood. This attitude is not carefree. Firstly, those tests are rather slow. It might be an issue when the number of tests will increase. We use a real database connection that has an overhead.
Secondly, those tests are not as stable as the isolated ones. We have to remember about launching the database before running tests, running all migrations, and (sometimes) purging tables. If something can break apart - it will eventually happen. If we want to have a useful CI, we have to run those tests there as well. We need to configure the CI the same way we did it on our local machines. The setup is much more complicated than just running go test ./....
It is confirmed that integration tests are helpful. Unit tests should be the base of our tests’ sets. This knowledge motivate us to write them. We have to understand the core domain first. From the order of requests we send, we can assume that creating the project is the starting point. Take a look at the handler below.
func (p Project) Create(w http.ResponseWriter, r *http.Request) {
b, err := ioutil.ReadAll(r.Body)
if err != nil {
log.Printf("cannot read the body: %s", err)
http.Error(w, "cannot read the body", http.StatusBadRequest)
return
}
req := httpmodels.CreateProjectRequest{}
err = json.Unmarshal(b, &req)
if err != nil {
log.Printf("cannot read the body: %s", err)
http.Error(w, "invalid JSON provided", http.StatusBadRequest)
return
}
if req.Name == "" {
log.Printf("the name is required")
http.Error(w, "the name is required", http.StatusBadRequest)
return
}
id, err := p.Repo.CreateProject(req.Name)
if err != nil {
log.Printf("internal server error: %s", err)
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
resp := httpmodels.CreateProjectResponse{id}
b, _ = json.Marshal(resp)
w.Header().Add("content-type", "application/json")
w.WriteHeader(http.StatusOK)
_, _ = w.Write(b)
}
First lines aren’t very useful at this point. It’s only standard reading the request and unmarshalling to a structure. We can see an if statement that looks a little bit suspicious.
if req.Name == "" {
log.Printf("the name is required")
http.Error(w, "the name is required", http.StatusBadRequest)
return
}
It says we need to add the name and it is absolutely necessary. When we continue reading, we will notice that we return the id of the project to the API caller. The id is downloaded from the function that creates the project. To create a new scheme we have to enter its name. Every project has an ID. I will show you how to model this in the code.
type Project struct {
id string
name string
}
func (p Project) Name() string {
return p.name
}
func (p Project) ID() string {
return p.id
}
We created a new structure with private methods. It will provide the correct state of the project and won’t cause any problems. We use private fields, which we recived by writing two getter methods. They don’t have constructors. Although we can still create a custom constructor function.
In our domain, the project has to have a valid name and an ID. We can achieve this in at least two ways. The first one is creating the constructor method. This method will do all the audits. The second approach is to create a function func (p Project) IsValid() bool. We’ll use it everytime we want to check if the project is an important object.
Personally, I prefer the first option, but the second one is valid as well. It’s all about preferences and specific of the case. Now, you are able to do the test. Create a new file called domain/project_test.go and put the test as shown below. Please notice that we created a new domain package.
package domain
import "testing"
func TestProject_Test_Validation(t *testing.T) {
testCases := map[string]struct {
id string
name string
}{
"empty ID": {
name: "jfslfjal",
},
"empty name": {
id: "jfslfjal",
},
}
for _, tc := range testCases {
_, err := NewProject(tc.id, tc.name)
if err == nil {
t.Error("expected that the validation fails but got no error")
}
}
}
We have to make sure that we check all the requirements. The test become red (doesn’t compile). That means there’s no such a NewProject yet. At this point you have to add it in domain/project.go file.
func NewProject(id, name string) (Project, error) {
if id == "" {
return Project{}, errors.New("the ID cannot be empty")
}
if name == "" {
return Project{}, errors.New("the name cannot be empty")
}
return Project{id: id, name: name}, nil
}
The test should change into green now. We extracted the first part of the domain! The domain can not be combined with other parts of the code directly. We need an additional layer. Now we will create a new package and call it the app (for an application layer).
When we take a look at the HTTP handler for creating a project we’ll notice a simple flow: the user provides the name, we create a new project, and return its ID. We should write a test that will model it.
package app
import (
"context"
"github.com/bkielbasa/gotodo/domain"
"github.com/google/uuid"
"testing"
)
func TestAddNewProject(t *testing.T) {
name := "my name:" + uuid.New().String()
ctx := context.Background()
projectServ := NewProjectService()
p, err := projectServ.Add(ctx, name)
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
if p.ID() == "" {
t.Errorf("ID is empty")
}
if name != p.Name() {
t.Errorf("name don't match, expected (%s) but got (%s)", name, p.Name())
}
}
At this point we create a new application service. The service job is to accept the name of the project and return a freshly created project followed by an error (if occurs). After that, we have to make sure that the name is as we provided, and the ID isn’t an empty string (this is what we know about the ID right now). You can see that the test doesn’t compile. This is how to make it work.
type ProjectService struct {}
func NewProjectService() ProjectService {
return ProjectService{}
}
func (serv ProjectService) Add(ctx context.Context, name string) (domain.Project, error) {
return domain.Project{}, nil
}
We create the missing constructor function for our new type - the application service. The service has a simple method with initial code - to make the code compile. When we run the test, we’ll notice that it fails. It is not surprising because we did nothing in the Add function.
func (serv ProjectService) Add(ctx context.Context, name string) (domain.Project, error) {
id := "gopher"
return domain.NewProject(id, name)
}
From now, the test is green. We can add one more test that will check if we wrote the name correctly.
func TestAddNewProjectWithEmptyName(t *testing.T) {
name := ""
projectServ := NewProjectService()
_, err := projectServ.Add(context.Background(), name)
if err == nil {
t.Errorf("expected error but got nil")
}
}
The test should be green. We didn’t check it correctly, so we have to change it. We’ll update the first test with getting a project for the particular ID and check if the Get() method still returns the same project.
func TestAddNewProject(t *testing.T) {
name := "my name:" + uuid.New().String()
ctx := context.Background()
projectServ := NewProjectService()
p, err := projectServ.Add(ctx, name)
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
if p.ID() == "" {
t.Errorf("ID is empty")
}
if name != p.Name() {
t.Errorf("name don't match, expected (%s) but got (%s)", name, p.Name())
}
p2, err := projectServ.Get(ctx, p.ID())
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
if p.ID() != p2.ID() {
t.Errorf("expected ID %s but %s given", p.ID(), p2.ID())
}
if p.Name() != p2.Name() {
t.Errorf("expected name %s but %s given", p.Name(), p2.Name())
}
}
As you can see, the code looks quite unreadable. We can fix the code by providing a helper function requireProject.
func TestAddNewProject(t *testing.T) {
name := "my name:" + uuid.New().String()
ctx := context.Background()
projectServ := NewProjectService(newStoreMock())
p, err := projectServ.Add(ctx, name)
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
checkProjectName(t, p, name)
p2, err := projectServ.Get(ctx, p.ID())
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
checkProjectName(t, p2, p.Name())
checkProjectID(t, p2, p.ID())
}
func checkProjectID(t *testing.T, p domain.Project, expectedID string) {
if p.ID() != expectedID {
t.Errorf("expected ID %s but %s given", expectedID, p.ID())
}
}
func checkProjectName(t *testing.T, p domain.Project, expectedName string) {
if p.Name() != expectedName {
t.Errorf("expected name %s but %s given", expectedName, p.Name())
}
}
It looks much better now, but the code doesn’t compile. To fix it we have to add the missing Get function.
func (serv ProjectService) Get(ctx context.Context, id string) (domain.Project, error) {
return domain.NewProject(id, "fjsfsl")
}
The test is still red. To make it work, we have to add storage that will keep the list of projects we created with the ability to fetch it back. This is how I designed its interface and update Add() and Get() functions to use.
type Repository interface {
Store(ctx context.Context, p domain.Project) error
Get(ctx context.Context, id string) (domain.Project, error)
}
func (serv ProjectService) Add(ctx context.Context, name string) (domain.Project, error) {
id := "gopher"
p, err := domain.NewProject(id, name)
if err != nil {
return domain.Project{}, err
}
err = serv.storage.Store(ctx, p)
if err != nil {
return domain.Project{}, err
}
return p, err
}
func (serv ProjectService) Get(ctx context.Context, id string) (domain.Project, error) {
return serv.storage.Get(ctx, id)
}
The ProjectService doesn’t contain the new functionality. We should add it now.
type ProjectService struct {
repo Repository
}
func NewProjectService(storage Repository) ProjectService {
return ProjectService{storage: storage}
}
It’s almost done. We just have to put the new dependency everywhere we create a new ProjectService struct. We need a new struct that will implement the interface. Let’s create a new one with a map that will hold the instances of domain.Project.
type repoMock struct {
data map[string]domain.Project
}
func newRepoMock() *storeMock {
return &repoMock{
data: make(map[string]domain.Project),
}
}
func (s *repoMock) Store(ctx context.Context, p domain.Project) error {
s.data[p.ID()] = p
return nil
}
func (s *repoMock) Get(ctx context.Context, id string) (domain.Project, error) {
return s.data[id], nil
}
It’s green again! I would add one more test because we did not cover one important case. What if the project doesn’t exist? Shouldn’t Get function return an error? The storage knows if the project exists or not so the error should come from it. We should create a separate error just for this case.
// in app/project.go
var ErrProjectNotFound = errors.New("the project is not found")
To make our testing easier, we need to add a new error to the mock storeMock and create a new method to set the given error.
type repoMock struct {
data map[string]domain.Project
err error // new field
}
func (s *repoMock) Get(ctx context.Context, id string) (domain.Project, error) {
return s.data[id], s.err // added the error here
}
func (s *repoMock) withError(err error) *storeMock {
s.err = err
return s
}
Now it’s safe because of new helper methods. We can easily write a test.
func TestAGetNotExistingProject(t *testing.T) {
id := "not exists"
ctx := context.Background()
storage := newRepoMock().withError(ErrProjectNotFound)
projectServ := NewProjectService(storage)
_, err := projectServ.Get(ctx, id)
if !errors.Is(err, ErrProjectNotFound) {
t.Errorf("expected error ErrProjectNotFound but got %v", err)
}
}
The job is almost done now. You should notice that we have a hardcoded ID for every project ID: gopher. We need to prepare a test that will force us to make it work.
func TestEveryProjectShouldHaveUniqueID(t *testing.T) {
name := "a name"
projectServ := NewProjectService(newRepoMock())
p1, err := projectServ.Add(context.Background(), name)
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
p2, err := projectServ.Add(context.Background(), name)
if err != nil {
t.Errorf("expected no error but got: %s", err)
}
if p1.ID() == p2.ID() {
t.Error("every project should have a unique ID")
}
}
It’s red now. There are many ways to generate a unique ID. To eliminate the red we’ll use the simple method - uuid.
id := uuid.New().String()
That’s all! We have passed the test. We extracted the domain from the current code. Of course, it’s not the whole business logic we have to refactor, but it’s a good starting point. You can find the difference of our change in this pull request. If you have any questions or suggestions about this part, there’s a comments section below. See you soon!
PS. If you want know more about Domain-Driven Desing, I can suggest this book by Eric Evans. (#ad).
Buy me a coffeeTags:
#tests
#ddd