Writing tests doesn't make you faster. Writing the RIGHT tests does. These laws show you which tests increase velocity—and which ones kill it.
Tests are hermits
No shared state, no execution order, no hidden coupling.
Read the guide →A slow test is already dead
Fast tests get run. Slow tests get skipped.
Read the guide →Flaky tests are worse than no tests
Same input, same output. Every single time.
Read the guide →Fail loudly, fail obviously
When a test fails, you should know exactly what broke and why.
Read the guide →One failure reason per test
When it breaks, you know exactly what broke.
Read the guide →Tests should survive refactoring
Test what your code promises, not how it delivers.
Read the guide →Every line of setup is a smell
Test data should be minimal and relevant to the assertion.
Read the guide →Test your code, fake the world
Mock I/O and external systems. Don't mock your own logic.
Read the guide →Delete tests that don't pull their weight
If a test doesn't pull its weight, delete it.
Read the guide →Tests are approximations of user experience. They don't make software more reliable by themselves—they increase developer velocity by giving you fast feedback about whether your changes break things.
High-value tests give you confidence to ship faster. Low-value tests slow you down with noise, maintenance burden, and false signals. These laws help you tell the difference.