smoke test

The name comes from hardware: power the board up and see whether smoke comes out. It is the cheapest possible question — does this thing run at all — and it catches a category of failure that nothing earlier in a verification chain can.

Code can typecheck, pass its tests and build cleanly, and still die the moment it starts. A missing environment variable. An import that only resolves in development. A database client constructed at module load against a URL that is not there. Every one of those is invisible to a compiler and obvious to a process that tries to boot.

A smoke test is not an end-to-end test. It does not check that the booking form saves a booking or that the prices are right; it checks that the application started and returned a page. Confusing the two is how people end up believing a passing build means a working product.

In sup3rapp it is the fourth and final stage, measured at 3.9 seconds on our marketing-site scaffold in a network-less sandbox. It is the last thing that stands between a generated build and your preview.