Cut the CRAP

What is CRAP?

CRAP (Change Risk Anti-Patterns) measures how risky a function is to change. It combines two factors: cyclomatic complexity (how many branches/paths) and test coverage (how much is exercised by automated tests).

Formula: CRAP(m) = comp(m)^2 * (1 - cov(m)/100)^3 + comp(m)

Reading the score:

• 1 -- trivial function, well tested. No risk.
• < 30 -- acceptable. Safe to change.
• > 30 -- CRAPpy. Too complex for its test coverage. High risk of breaking when modified.

A function with 0% coverage only needs complexity > 5 to be CRAPpy. A function with 100% coverage can have complexity up to 30 before crossing the threshold. The metric rewards either simplifying code or testing it -- ideally both.

Workflow

Phase 1 -- Measure