Building a finance tracking REST API using Go with TDD - Part 2
Tags: go, rest, api, tdd
Published: 2018-09-17 20:21:51

---
title: Building a finance tracking REST API using Go with TDD - Part 2
published: true
description: Building a finance tracking REST API using Go from scratch with test-driven development
tags: go, rest, api, tdd
---

Hola amigos! In this part we're going to complete budgets API, also I'm going to tell you in recent days I've come up with a great combination of tools to build REST APIs much more MVC-like than this that I'm going to write about in incoming posts.


I've just finished with just one single acceptance test for budgets API but here I going to declare various test cases should cover almost 100% of budgets API behaviors. So let's get started:

```go
// budgets_test.go
package main

import (
	"net/http"
	"os"
	"testing"

	"github.com/azbshiri/common/test"
	"github.com/go-pg/pg"
	"github.com/go-pg/pg/orm"
	"github.com/gorilla/mux"
	"github.com/pquerna/ffjson/ffjson"
	"github.com/stretchr/testify/assert"
)

var testServer *server
var badServer *server

func TestMain(m *testing.M) {
	testServer = newServer(
		pg.Connect(&pg.Options{
			User:     "alireza",
			Password: "alireza",
			Database: "alireza_test",
		}),
		mux.NewRouter(),
	)

	badServer = newServer(
		pg.Connect(&pg.Options{
			User:     "not_found",
			Password: "alireza",
			Database: "alireza",
		}),
		mux.NewRouter(),
	)

        // Here we create a temporary table to store each test case
        // data and follow isolation which would be dropped after.
	testServer.db.CreateTable(&budget{}, &orm.CreateTableOptions{
		Temp: true,
	})

	os.Exit(m.Run())
}

func TestGetBudgets_EmptyResponse(t *testing.T) {
	var body []budget
	res, err := test.DoRequest(testServer, "GET", BudgetPath, nil)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Len(t, body, 0)
	assert.Equal(t, res.Code, http.StatusOK)
}

func TestGetBudgets_NormalResponse(t *testing.T) {
	var body []budget
	budgets, err := CreateBudgetListFactory(testServer.db, 10)
	assert.NoError(t, err)

	res, err := test.DoRequest(testServer, "GET", BudgetPath, nil)
	assert.Equal(t, http.StatusOK, res.Code)
	assert.NoError(t, err)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.Len(t, body, 10)
	assert.Equal(t, budgets, &body)
}

func TestGetBudgets_DatabaseError(t *testing.T) {
	var body Error
	res, err := test.DoRequest(badServer, "GET", BudgetPath, nil)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Equal(t, DatabaseError, &body)
	assert.Equal(t, http.StatusInternalServerError, res.Code)
}
```

I've defined three test cases normal response, empty response and when there's a database error that we've simulated using a non-existing database username to make database unavailable. Also as you noticed there's a `DatabaseError` constant which assert to make sure errors are readable. I've created a `errors.go` file in which there are a new error type called `Error` as below:

```
package main

import "net/http"

type Error struct {
	Message string `json:"message"`
	Status  int    `json:"status"`
}

func Err(message string, status int) *Error {
	return &Error{message, status}
}

var DatabaseError = Err("Your request failed due to a database error.", http.StatusInternalServerError)
```

It carries a message and a corresponding HTTP code to make dealing with errors easier. Now that everything is in a right place we should pass or tests which are failing in the current state.

So first we go by creating an HTTP handler function in `budgets.go` file:

```go
// budgets.go
package main

import (
	"net/http"

	"github.com/azbshiri/common/db"
)

type budget struct {
	db.Model
	Amount float64 `json:"amount"`
}

func (s *server) getBudgets(w http.ResponseWriter, r *http.Request) {
}
```

Then registering the HTTP handle in `routes.go`:

```go
// routes.go
package main

const BudgetPath = "/api/budgets"

func (s *server) routes() {
	s.mux.HandleFunc(BudgetPath, s.getBudgets).Methods("GET")
}
```

Note: I defined `BudgetPath` constant to be able to use budgets API path in various places including tests. Tests are still failing so we should get budgets from the database and return an acceptable response to consumers. Also, I created a `CreateBudgetListFactory` factory in `factories.go` file to making database population easier.

```go
// factories.go
package main

import (
	"math/rand"
	"time"

	"github.com/go-pg/pg"
)

func CreateBudgetListFactory(db *pg.DB, length int) (*[]budget, error) {
	budgets := make([]budget, length)
	for _, budget := range budgets {
		budget.Amount = rand.Float64()
		budget.CreatedAt = time.Now()
	}

	err := db.Insert(&budgets)
	if err != nil {
		return nil, err
	}

	return &budgets, nil
}
```

```go
// budgets.go
package main

import (
	"encoding/json"
	"net/http"

	"github.com/azbshiri/common/db"
	"github.com/pquerna/ffjson/ffjson"
)

type budget struct {
	db.Model
	Amount float64 `json:"amount"`
}

func (s *server) getBudgets(w http.ResponseWriter, r *http.Request) {
	var budgets []*budget
	err := s.db.Model(&budgets).Select()
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		json.NewEncoder(w).Encode(DatabaseError)
		return
	}

	ffjson.NewEncoder(w).Encode(budgets)
}
```

Now we're green:

```
=== RUN   TestGetBudgets_EmptyResponse
--- PASS: TestGetBudgets_EmptyResponse (0.00s)
=== RUN   TestGetBudgets_NormalResponse
--- PASS: TestGetBudgets_NormalResponse (0.00s)
=== RUN   TestGetBudgets_DatabaseError
--- PASS: TestGetBudgets_DatabaseError (0.00s)
PASS
ok      github.com/azbshiri/budget-api  0.040s
```
![one cannot simply make tests pass](https://i.imgflip.com/2i56ol.jpg)

Okay, now we repeating the same steps for creating a new budget API:

```go
// budgets_test.go
package main

import (
	"bytes"
	"net/http"
	"os"
	"testing"

	"github.com/azbshiri/common/test"
	"github.com/go-pg/pg"
	"github.com/go-pg/pg/orm"
	"github.com/gorilla/mux"
	"github.com/pquerna/ffjson/ffjson"
	"github.com/stretchr/testify/assert"
)

var testServer *server
var badServer *server

func TestMain(m *testing.M) {
	testServer = newServer(
		pg.Connect(&pg.Options{
			User:     "alireza",
			Password: "alireza",
			Database: "alireza_test",
		}),
		mux.NewRouter(),
	)

	badServer = newServer(
		pg.Connect(&pg.Options{
			User:     "not_found",
			Password: "alireza",
			Database: "alireza",
		}),
		mux.NewRouter(),
	)

	testServer.db.CreateTable(&budget{}, &orm.CreateTableOptions{
		Temp: true,
	})

	os.Exit(m.Run())
}

func TestGetBudgets_EmptyResponse(t *testing.T) {
	var body []budget
	res, err := test.DoRequest(testServer, "GET", BudgetPath, nil)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Len(t, body, 0)
	assert.Equal(t, res.Code, http.StatusOK)
}

func TestGetBudgets_NormalResponse(t *testing.T) {
	var body []budget
	budgets, err := CreateBudgetListFactory(testServer.db, 10)
	assert.NoError(t, err)

	res, err := test.DoRequest(testServer, "GET", BudgetPath, nil)
	assert.Equal(t, http.StatusOK, res.Code)
	assert.NoError(t, err)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.Len(t, body, 10)
	assert.Equal(t, budgets, &body)
}

func TestGetBudgets_DatabaseError(t *testing.T) {
	var body Error
	res, err := test.DoRequest(badServer, "GET", BudgetPath, nil)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Equal(t, DatabaseError, &body)
	assert.Equal(t, http.StatusInternalServerError, res.Code)
}

func TestCreateBudget(t *testing.T) {
	var body budget
	byt, err := ffjson.Marshal(&budget{Amount: 1000.4})
	rdr := bytes.NewReader(byt)

	res, err := test.DoRequest(testServer, "POST", BudgetPath, rdr)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Equal(t, 1000.4, body.Amount)
	assert.Equal(t, http.StatusOK, res.Code)
}

func TestCreateBudget_BadParamError(t *testing.T) {
	var body Error
	res, err := test.DoRequest(testServer, "POST", BudgetPath,
		bytes.NewReader([]byte{}))

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Equal(t, BadParamError, &body)
	assert.Equal(t, http.StatusBadRequest, res.Code)
}

func TestCreateBudget_DatabaseError(t *testing.T) {
	var body Error
	byt, err := ffjson.Marshal(&budget{Amount: 1000.4})
	rdr := bytes.NewReader(byt)

	res, err := test.DoRequest(badServer, "POST", BudgetPath, rdr)

	ffjson.NewDecoder().DecodeReader(res.Body, &body)
	assert.NoError(t, err)
	assert.Equal(t, DatabaseError, &body)
	assert.Equal(t, http.StatusInternalServerError, res.Code)
}
```

Creating a new HTTP handle function for new API:
```go
// budgets.go
package main

import (
	"encoding/json"
	"net/http"

	"github.com/azbshiri/common/db"
	"github.com/pquerna/ffjson/ffjson"
)

type budget struct {
	db.Model
	Amount float64 `json:"amount"`
}

func (s *server) getBudgets(w http.ResponseWriter, r *http.Request) {
	var budgets []*budget
	err := s.db.Model(&budgets).Select()
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		json.NewEncoder(w).Encode(DatabaseError)
		return
	}

	ffjson.NewEncoder(w).Encode(budgets)
}

func (s *server) createBudget(w http.ResponseWriter, r *http.Request) {
	var param struct {
		Amount float64 `json:"amount"`
	}
	err := ffjson.NewDecoder().DecodeReader(r.Body, &param)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		json.NewEncoder(w).Encode(BadParamError)
		return
	}

	budget := budget{Amount: param.Amount}
	err = s.db.Insert(&budget)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		json.NewEncoder(w).Encode(DatabaseError)
		return
	}

	ffjson.NewEncoder(w).Encode(budget)
}
```

Note: I used DTO concept to decode parameters that sent to budget creation API, which is a great way to do so.

And we're done:
```
=== RUN   TestGetBudgets_EmptyResponse
--- PASS: TestGetBudgets_EmptyResponse (0.01s)
=== RUN   TestGetBudgets_NormalResponse
--- PASS: TestGetBudgets_NormalResponse (0.00s)
=== RUN   TestGetBudgets_DatabaseError
--- PASS: TestGetBudgets_DatabaseError (0.00s)
=== RUN   TestCreateBudget
--- PASS: TestCreateBudget (0.00s)
=== RUN   TestCreateBudget_BadParamError
--- PASS: TestCreateBudget_BadParamError (0.00s)
=== RUN   TestCreateBudget_DatabaseError
--- PASS: TestCreateBudget_DatabaseError (0.00s)
PASS
ok      github.com/azbshiri/budget-api  (cached)
```

Please add your comments down below and if you found this informative don't forget to drop a heart for me :D