codegen: move generated test helpers to new 'db_test.go' file

pkg/codegen/tpl/db_test.go.tpl

@@ -0,0 +1,19 @@
+package db_test
+
+import (
+	"fmt"
+
+	. "git.offline-twitter.com/offline-labs/gas-stack/pkg/flowutils"
+
+	. "{{ .ModuleName }}/pkg/db"
+)
+
+var TestDB *DB
+
+func init() {
+	TestDB = MakeDB("tmp")
+}
+func MakeDB(dbName string) *DB {
+	db := Must(Create(fmt.Sprintf("file:%s?mode=memory&cache=shared", dbName)))
+	return db
+}