Writing Reliable Regular Expression Code with Python Unit Tests

Bolster Confidence in Your RE Patterns Through Automated Checks

Max N
3 min readApr 6, 2024

Unit testing represents a crucial component of modern software development workflows, providing developers with the ability to validate assumptions, catch regressions early, and sleep better knowing their creations perform as intended.

Regular expressions pose unique challenges when attempting to unit test owing to their compact syntax, hidden states, and occasional opacity. Luckily, Python’s built-in unittest module paired with some creativity makes short work of otherwise daunting hurdles.

Join us as we explore techniques for crafting robust unit tests around regular expressions, ultimately increasing developer satisfaction and project longevity.

Creating Simple Unit Tests for Basic Patterns

At first glance, testing regular expressions seems trivial — either the pattern matches the desired input or it doesn’t. But digging deeper, numerous failure modes await unsuspecting coders who assume too much.

Careful consideration of boundary cases, partially matching inputs, and negative assertions contribute significantly to improved code stability.

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Max N

A writer that writes about JavaScript and Python to beginners. If you find my articles helpful, feel free to follow.