graph/db: refactor to make postgres fixtures re-usable

In preparation for tests where we will want to spin up SQL DBs many
times, we do some refactoring so that it is easy to re-use postgres
fixtures since those are expensive to spin up.

graph/db/test_postgres.go

@@ -6,9 +6,46 @@ import (
 	"database/sql"
 	"testing"
 
+	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/lightningnetwork/lnd/sqldb"
+	"github.com/stretchr/testify/require"
 )
 
+// NewTestDB is a helper function that creates a SQLStore backed by a SQL
+// database for testing.
+func NewTestDB(t testing.TB) V1Store {
+	return NewTestDBWithFixture(t, nil)
+}
+
+// NewTestDBFixture creates a new sqldb.TestPgFixture for testing purposes.
+func NewTestDBFixture(t *testing.T) *sqldb.TestPgFixture {
+	pgFixture := sqldb.NewTestPgFixture(t, sqldb.DefaultPostgresFixtureLifetime)
+	t.Cleanup(func() {
+		pgFixture.TearDown(t)
+	})
+	return pgFixture
+}
+
+// NewTestDBWithFixture is a helper function that creates a SQLStore backed by a
+// SQL database for testing.
+func NewTestDBWithFixture(t testing.TB, pgFixture *sqldb.TestPgFixture) V1Store {
+	var querier BatchedSQLQueries
+	if pgFixture == nil {
+		querier = newBatchQuerier(t)
+	} else {
+		querier = newBatchQuerierWithFixture(t, pgFixture)
+	}
+
+	store, err := NewSQLStore(
+		&SQLStoreConfig{
+			ChainHash: *chaincfg.MainNetParams.GenesisHash,
+		}, querier,
+	)
+	require.NoError(t, err)
+
+	return store
+}
+
 // newBatchQuerier creates a new BatchedSQLQueries instance for testing
 // using a PostgreSQL database fixture.
 func newBatchQuerier(t testing.TB) BatchedSQLQueries {
@@ -19,6 +56,14 @@ func newBatchQuerier(t testing.TB) BatchedSQLQueries {
 		pgFixture.TearDown(t)
 	})
 
+	return newBatchQuerierWithFixture(t, pgFixture)
+}
+
+// newBatchQuerierWithFixture creates a new BatchedSQLQueries instance for
+// testing using a PostgreSQL database fixture.
+func newBatchQuerierWithFixture(t testing.TB,
+	pgFixture *sqldb.TestPgFixture) BatchedSQLQueries {
+
 	db := sqldb.NewTestPostgresDB(t, pgFixture).BaseDB
 
 	return sqldb.NewTransactionExecutor(