Starting points from here:

Tips for a good line of sight:

• Align the happy path to the left; you should quickly be able to scan down one column to see the expected execution flow
• Don’t hide happy path logic inside a nest of indented braces
• Exit early from your function
• Avoid else returns; consider flipping the if statement
• Put the happy return statement as the very last line
• Extract functions and methods to keep bodies small and readable
• If you need big indented bodies, consider giving them their own function
• The DRY principle stands for “Don’t Repeat Yourself” and requires that any piece of domain knowledge has a single representation in your code base.

Unit Testing

Only allow the most valuable tests in your test suite; disregard the rest. Vladimir Khorikov