Now that the project has come ahead a bit, we should make sure everything is easily maintainable and reproducible. Thus, test-driven development is highly required, i.e. for all new functionality ending up in the master, provide proper unit tests. As long as this project is python-based, I suggest to just use pytest, and to have a dedicated test folder.
Second, these tests should be automatically run upon merges or also commits. I suggest travis for this.