Make a lazy loading for opening a connection

In the current approach, the connection logic is only triggered at the
moment of immediate need for connection.

We also get a single connection opening point.

testingpg/testingpg.go

@@ -28,6 +28,8 @@ func New(t TestingT) *Postgres {
 }
 
 type Postgres struct {
+	t TestingT
+
 	url string
 	ref string
 
@@ -51,6 +53,8 @@ func newPostgres(t TestingT) *Postgres {
 	require.NoError(t, err)
 
 	return &Postgres{
+		t: t,
+
 		url: urlStr,
 		ref: refDatabase,
 
@@ -63,26 +67,28 @@ func (p *Postgres) URL() string {
 }
 
 func (p *Postgres) PgxPool() *pgxpool.Pool {
-	return p.conn
+	pool, err := pgxpool.New(context.Background(), p.URL())
+	require.NoError(p.t, err)
+
+	// Automatically close connection after the test is completed.
+	p.t.Cleanup(func() {
+		pool.Close()
+	})
+
+	return pool
 }
 
 func (p *Postgres) cloneFromReference(t TestingT) *Postgres {
-	cfg, err := pgxpool.ParseConfig(p.url)
-	require.NoError(t, err)
-
-	pool, err := pgxpool.New(context.Background(), p.url)
-	require.NoError(t, err)
-
 	newDatabaseName := uuid.New().String()
 
-	const sqlTemplate = `CREATE DATABASE %q WITH TEMPLATE %s OWNER %s;`
+	const sqlTemplate = `CREATE DATABASE %q WITH TEMPLATE %s;`
 	sql := fmt.Sprintf(
 		sqlTemplate,
 		newDatabaseName,
 		p.ref,
-		cfg.ConnConfig.User,
 	)
-	_, err = pool.Exec(context.Background(), sql)
+
+	_, err := p.PgxPool().Exec(context.Background(), sql)
 	require.NoError(t, err)
 
 	// Automatically drop database copy after the test is completed.
@@ -96,20 +102,17 @@ func (p *Postgres) cloneFromReference(t TestingT) *Postgres {
 		require.NoError(t, err)
 	})
 
-	urlString := replaceDBName(t, cfg, newDatabaseName)
+	urlString := replaceDBName(t, p.URL(), newDatabaseName)
-	newPool, err := pgxpool.New(context.Background(), urlString)
-	require.NoError(t, err)
 
 	return &Postgres{
+		t:   p.t,
 		url: urlString,
 		ref: newDatabaseName,
-
-		conn: newPool,
 	}
 }
 
-func replaceDBName(t TestingT, cfg *pgxpool.Config, dbname string) string {
+func replaceDBName(t TestingT, dataSourceURL, dbname string) string {
-	r, err := url.Parse(cfg.ConnString())
+	r, err := url.Parse(dataSourceURL)
 	require.NoError(t, err)
 	r.Path = dbname
 	return r.String()