Example persistence tests for Golang - Blog post

main_test.go

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/go-sql-driver/mysql"
	"github.com/google/go-cmp/cmp"
	"github.com/ory/dockertest/v3"
	"testing"
)

// RootUser the default name of MySQL root user. We run tests in root because we don't have to worry about privileges.
// Disclaimer: We run on root because of testing simplicity.
const RootUser = "root"

// DockerRepository is reference to Docker Hub's Repository.
const DockerRepository = "mysql"

// Version is a version of MySQL. Available versions are located on for DockerRepository Docker Hub.
const Version = "8.0"

// AllowEmptyPassword is a simple setup for valid connection for root user.
// Disclaimer: Do not use it on production but for tests it looks fine if you don't have specific requirements.
const AllowEmptyPassword = "MYSQL_ALLOW_EMPTY_PASSWORD=yes"

// Environments are passed into MySQL instance.
var Environments = []string{
	AllowEmptyPassword,
}

// pool holds reference to Docker.
var pool *dockertest.Pool

// init initialize docker pool.
func init() {
	var p, err = dockertest.NewPool("")
	if err != nil {
		panic(err)
	}

	pool = p
}

// mysqlContainer creates Docker container with MySQL and wait until MySQL is ready.
func mysqlContainer() (*sql.DB, *dockertest.Resource, error) {
	rootUser := RootUser

	container, err := pool.RunWithOptions(&dockertest.RunOptions{
		Repository: DockerRepository,
		Tag:        Version,
		Env:        Environments,
	})
	if err != nil {
		return nil, nil, err
	}

	// get mapped port
	mysqlHostPort := container.GetPort("3306/tcp")

	var db *sql.DB

	// wait until MySQL is ready
	if err := pool.Retry(func() error {
		var err error
		// connect with MySQL using port available in host
		db, err = sql.Open("mysql", fmt.Sprintf("%s@(localhost:%s)/mysql", rootUser, mysqlHostPort))
		if err != nil {
			return err
		}
		if err := db.Ping(); err != nil {
			return err
		}

		return nil
	}); err != nil {
		return nil, container, err
	}

	return db, container, nil
}

// getMessages returns messages from database.
func getMessages(db *sql.DB) ([]string, error) {
	messages := make([]string, 0)

	rows, err := db.Query("SELECT message FROM demo")
	if err != nil {
		return nil, err
	}

	defer rows.Close()
	for rows.Next() {
		var msg string

		if err := rows.Scan(&msg); err != nil {
			continue
		}

		messages = append(messages, msg)
	}

	err = rows.Err()
	if err != nil {
		return messages, err
	}

	return messages, nil
}

// seed is useful to prepare database with data before queries.
func seed(db *sql.DB, message string) error {
	if _, err := db.Query(`
		create table demo(
		   id INT NOT NULL AUTO_INCREMENT,
		   message VARCHAR(100) NOT NULL,
		   PRIMARY KEY ( id )
		);
	`); err != nil {
		return err
	}

	query, err := db.Prepare(`
		insert into demo(message) values (?);
	`)
	if err != nil {
		return err
	}
	if _, err := query.Exec(message); err != nil {
		return err
	}

	return nil
}

// beforeEach is a small helper function to run ephemeral environment for each test run.
func beforeEach(tx *testing.T) (db *sql.DB, done func(), err error) {
	var container *dockertest.Resource

	db, container, err = mysqlContainer()
	if err != nil {
		tx.Fatal(err)
		return
	}

	done = func() {
		if err := container.Close(); err != nil {
			tx.Fatal(err)
		}
	}

	return
}

// diff returns error message if expected is different from current.
func diff(expected interface{}, current interface{}) error {
	if d := cmp.Diff(expected, current); d != "" {
		return fmt.Errorf("%s mismatch (-want +got):\n%s", "messages are not equal", d)
	}

	return nil
}

func TestMySQLInsert(tx *testing.T) {
	tx.Run("Insert and query messages from database", func(t *testing.T) {
		db, done, err := beforeEach(tx)
		if done != nil {
			defer done()
		}
		if err != nil {
			tx.Fatal(err)
			return
		}

		if err := seed(db, "hello world"); err != nil {
			t.Fatal(err)
			return
		}
		messages, err := getMessages(db)
		if err != nil {
			t.Log(err)
		}

		expected := []string{"hello world"}

		if err := diff(expected, messages); err != nil {
			t.Fatal(err)
		}
	})
}