Add docker-test support for SQLServer

This commit adds the last step for running all integration tests
with zero database setup =]

main_test.go

@@ -30,6 +30,8 @@ func TestMain(m *testing.M) {
 	connectionString["postgres"] = postgresURL
 	mysqlURL, closeMySQL := startMySQLDB("ksql")
 	connectionString["mysql"] = mysqlURL
+	sqlServerURL, closeSQLServer := startSQLServerDB("ksql")
+	connectionString["sqlserver"] = sqlServerURL
 
 	exitCode := m.Run()
 
@@ -37,6 +39,7 @@ func TestMain(m *testing.M) {
 	// of the os.Exit call below:
 	closePostgres()
 	closeMySQL()
+	closeSQLServer()
 
 	os.Exit(exitCode)
 }
@@ -155,6 +158,62 @@ func startMySQLDB(dbName string) (databaseURL string, closer func()) {
 	}
 }
 
+func startSQLServerDB(dbName string) (databaseURL string, closer func()) {
+	// uses a sensible default on windows (tcp/http) and linux/osx (socket)
+	pool, err := dockertest.NewPool("")
+	if err != nil {
+		log.Fatalf("Could not connect to docker: %s", err)
+	}
+
+	// pulls an image, creates a container based on it and runs it
+	resource, err := pool.RunWithOptions(
+		&dockertest.RunOptions{
+			Repository: "mcr.microsoft.com/mssql/server",
+			Tag:        "2017-latest",
+			Env: []string{
+				"SA_PASSWORD=Sqls3rv3r",
+				"ACCEPT_EULA=Y",
+			},
+		},
+		func(config *docker.HostConfig) {
+			// set AutoRemove to true so that stopped container goes away by itself
+			config.AutoRemove = true
+			config.RestartPolicy = docker.RestartPolicy{Name: "no"}
+		},
+	)
+	if err != nil {
+		log.Fatalf("Could not start resource: %s", err)
+	}
+
+	hostAndPort := resource.GetHostPort("1433/tcp")
+	databaseUrl := fmt.Sprintf("sqlserver://sa:Sqls3rv3r@%s?databaseName=%s", hostAndPort, dbName)
+
+	fmt.Println("Connecting to sqlserver on url: ", databaseUrl)
+
+	resource.Expire(40) // Tell docker to hard kill the container in 20 seconds
+
+	var sqlDB *sql.DB
+	// exponential backoff-retry, because the application in the container might not be ready to accept connections yet
+	pool.MaxWait = 10 * time.Second
+	pool.Retry(func() error {
+		sqlDB, err = sql.Open("sqlserver", databaseUrl)
+		if err != nil {
+			return err
+		}
+		return sqlDB.Ping()
+	})
+	if err != nil {
+		log.Fatalf("Could not connect to docker: %s", err)
+	}
+	sqlDB.Close()
+
+	return databaseUrl, func() {
+		if err := pool.Purge(resource); err != nil {
+			log.Fatalf("Could not purge resource: %s", err)
+		}
+	}
+}
+
 func toJSON(i interface{}) []byte {
 	rawJSON, err := json.Marshal(i)
 	if err != nil {