Some references on software testing:

• An introduction to software testing
• A general guide to testing in Python
• A guide to unittest (PyUnit)
• …and another
• Some tricks with PyCharm:
  • running and debugging
  • python debugger
  • pycharm debug console
  • stepping through program
• Some tricks with Rstudio
• using R package testthat
• thoughts on input validation
• Tests for randomness
• Thinking a bit about what testing means.