Identify assumptions in your code
What assumptions/expectations exist on your data or (user) input?
What assumptions/expectations exist on the input of (a) function(s)?
Based on the assumptions/expectations you were able to identify, work on increasing the robustness of your code. Choose one:
Make the input/data assumptions explicit
Option 1: Explicitly state assumptions on data or input in your README.md.
Option 2: Write a piece of code that tests the validity of data/input, and reports an error if the expectations are not met.
Test the input for a function. Modify the code inside your function to:
check the value of the arguments passed to your function using if/else statements;
raise an error in case an argument is out of the range of acceptable values.