Clone postgres schema for each test

clone_postgres_schema_test.go

package my_package_test

import (
	"fmt"
	"testing"

	"github.com/gtforge/global_payment_manager_service/testdb"
	"github.com/stretchr/testify/require"
)

func TestUsingTestdbPrepare(t *testing.T) {
	t.Parallel()
	for i := 0; i < 10; i++ {
		t.Run(fmt.Sprintf("%d", i+1), func(t *testing.T) {
			t.Parallel()
			db, _ := testdb.Prepare(t)
			_, err := db.Exec("CREATE TABLE abc (id INT PRIMARY KEY)")
			require.NoError(t, err)
			_, err = db.Exec("INSERT INTO abc (id) VALUES ($1)", 123)
			require.NoError(t, err)
		})
	}
}

testdb.go

package testdb

import (
	"crypto/md5"
	"database/sql"
	"fmt"
	"regexp"
	"strings"
	"sync"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

var once sync.Once

func DSN() string {
	return "host=localhost port=5432 user=postgres password=postgres dbname=my_database sslmode=disable timezone=UTC"
}

// Prepare clones public schema (w/o data) and returns connection to new schema.
// The second returned parameter is schema name.
func Prepare(t *testing.T) (*sql.DB, string) {
	dsn := DSN()
	db, err := sql.Open("postgres", dsn)
	require.NoError(t, err)
	once.Do(func() {
		exec(t, db, createFunctionCloneSchema)
	})
	schema := strings.ToLower(regexp.MustCompile(`\W`).ReplaceAllString(t.Name(), "_"))
	const pqIdentifierMaxLength = 63
	if len(schema) > pqIdentifierMaxLength {
		schema = fmt.Sprintf("%s_%x", schema[:pqIdentifierMaxLength-md5.Size*2-1], md5.Sum([]byte(schema)))
		require.Len(t, schema, pqIdentifierMaxLength)
	}
	exec(t, db, "SELECT clone_schema('public', $1);", schema)
	err = db.Close()
	require.NoError(t, err)

	db, err = sql.Open("postgres", dsn+" search_path="+schema)
	require.NoError(t, err)
	t.Cleanup(func() {
		assert.NoError(t, db.Close())
	})

	return db, schema
}

func exec(t *testing.T, db *sql.DB, query string, args ...interface{}) {
	_, err := db.Exec(query, args...)
	require.NoError(t, err)
}

const createFunctionCloneSchema string = `--
BEGIN;
SELECT pg_advisory_xact_lock(2142616474639426746);

CREATE OR REPLACE FUNCTION public.clone_schema(source_schema text, dest_schema text)
    RETURNS void AS
$BODY$
DECLARE
    object               text;
    buffer               text;
    default_             text;
    column_              text;
    constraint_name_     text;
    constraint_def_      text;
    trigger_name_        text;
    trigger_timing_      text;
    trigger_events_      text;
    trigger_orientation_ text;
    trigger_action_      text;
BEGIN
    -- replace existing schema
    EXECUTE 'DROP SCHEMA IF EXISTS ' || dest_schema || ' CASCADE';
    -- create schema
    EXECUTE 'CREATE SCHEMA ' || dest_schema;
    -- create sequences
    FOR object IN
        SELECT sequence_name::text
        FROM information_schema.SEQUENCES
        WHERE sequence_schema = source_schema
        LOOP
            EXECUTE 'CREATE SEQUENCE ' || dest_schema || '.' || object;
        END LOOP;
    -- create tables
    FOR object IN
        SELECT table_name::text FROM information_schema.TABLES WHERE table_schema = source_schema
        LOOP
            buffer := dest_schema || '.' || object;
            -- create table
            EXECUTE 'CREATE TABLE ' || buffer || ' (LIKE ' || source_schema || '.' || object ||
                    ' INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING DEFAULTS)';
            -- fix sequence defaults
            FOR column_, default_ IN
                SELECT column_name::text,
                       REPLACE(column_default::text, source_schema || '.', dest_schema || '.')
                FROM information_schema.COLUMNS
                WHERE table_schema = dest_schema
                  AND table_name = object
                  AND column_default LIKE 'nextval(%' || source_schema || '.%::regclass)'
                LOOP
                    EXECUTE 'ALTER TABLE ' || buffer || ' ALTER COLUMN ' || column_ ||
                            ' SET DEFAULT ' || default_;
                END LOOP;
            -- create triggers
            FOR
            trigger_name_, trigger_timing_, trigger_events_, trigger_orientation_, trigger_action_ IN
                SELECT trigger_name::text,
                       action_timing::text,
                       string_agg(event_manipulation::text, ' OR '),
                       action_orientation::text,
                       action_statement::text
                FROM information_schema.TRIGGERS
                WHERE event_object_schema = source_schema
                  AND event_object_table = object
                GROUP BY trigger_name, action_timing, action_orientation, action_statement
                LOOP
                    EXECUTE 'CREATE TRIGGER ' || trigger_name_ || ' ' || trigger_timing_ || ' ' ||
                            trigger_events_ || ' ON ' || buffer || ' FOR EACH ' ||
                            trigger_orientation_ || ' ' || trigger_action_;
                END LOOP;
        END LOOP;
    -- reiterate tables and create foreign keys
    FOR object IN
        SELECT table_name::text FROM information_schema.TABLES WHERE table_schema = source_schema
        LOOP
            buffer := dest_schema || '.' || object;
            -- create foreign keys
            FOR constraint_name_, constraint_def_ IN
                SELECT conname::text,
                       REPLACE(pg_get_constraintdef(pg_constraint.oid), source_schema || '.',
                               dest_schema || '.')
                FROM pg_constraint
                         INNER JOIN pg_class ON conrelid = pg_class.oid
                         INNER JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace
                WHERE contype = 'f'
                  AND relname = object
                  AND nspname = source_schema
                LOOP
                    EXECUTE 'ALTER TABLE ' || buffer || ' ADD CONSTRAINT ' || constraint_name_ ||
                            ' ' || constraint_def_;
                END LOOP;
        END LOOP;
END;

$BODY$
    LANGUAGE plpgsql VOLATILE
                     COST 100;

COMMIT;
`