Reduce duplication in protobuffer test

Use a common module to keep the common procedures for the protobuffer test, this module is used as dependency by protobuffer importer+exporter test in order to avoid code duplication
Reduce duplication in protobuffer test

Use a common module to keep the common procedures for the protobuffer test, this module is used as dependency by protobuffer importer+exporter test in order to avoid code duplication