A methodology for building test suites that are fast, reliable, and actually useful. Inspired by the 12-Factor App, adapted for test excellence.
Tests are hermits
No shared state, no dependencies, no execution order.
Read the guide →Test names are documentation
test_user_cannot_purchase_alcohol_under_21() beats test_purchase_validation().
Read the guide →Fast tests get run
Slow tests get skipped. Dead simple.
Read the guide →Flaky tests are worse than no tests
Same input, same output. Always.
Read the guide →One test, one concern
When it fails, you know exactly what broke.
Read the guide →No 'works on my machine'
Tests run identically everywhere—locally, CI, containers.
Read the guide →Tests adapt to refactoring
Test the contract, not the implementation.
Read the guide →Delete bad tests ruthlessly
A bad test is worse than no test.
Read the guide →Mock the edges, not the core
Mock APIs and databases, never your own code.
Read the guide →Test data tells a story
Explicit > magic. Minimal > kitchen sink.
Read the guide →Failures should scream what's wrong
'Expected 2 items in cart, got 0' beats 'assertion failed'.
Read the guide →Coverage tells you what ran, not what works
Use mutation testing to verify your tests actually catch bugs.
Read the guide →Just like the 12-Factor App methodology revolutionized how we build cloud applications, these 12 factors represent the essential principles for building test suites that don't suck. Each factor addresses a specific testing anti-pattern that we've all suffered through.
Master these factors, and you'll write tests that are actually helpful rather than a burden. Your future self (and your team) will thank you.