From no tests to a passing suite in two prompts, with Claude Code

Watch two prompts take an untested Express API from no tests to a passing node:test suite, checked against the README.
Demo repo (agentshipped/notes-api): https://github.com/agentshipped/notes-api

The agent writes tests from the documented contract, not from the current code. I run the suite myself three times and decide for each failure whether the test or the code is wrong.
The second prompt makes the agent triage every failure against the README and never weaken a test; this run had no failures, so the source diff review is the real check.
You can copy the prompt structure (one task, named runner, README as contract, unhappy paths, acceptance command, no-weakening rule) and the source-only git diff review.
Not just JavaScript: the same technique works with pytest or go test, driven by the written contract and a no-weakening rule.
Tools: Claude Code, Node.js built-in test runner (node:test), Express, npm, git


Chapters:
0:00 Intro
0:15 The untested API
1:01 Read the store
1:41 Read the routes
2:24 Baseline run
3:02 Prompt one: write tests
3:46 First honest run
4:29 Prompt two: the review rule
5:20 Second run
5:57 Review the diff
6:45 Final measurement
7:25 Result