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Chapter 2: Run the demo app

Your agent clones mock-lab, starts the app and its database, and checks that the app answers all of the tutorial traffic.

Time: about 1 to 2 minutes.

Prompt​

Pick your language. The prompt is the same except for the directory.

Clone https://github.com/speedscale/mock-lab and open tutorial/go. Start its Postgres with docker compose, run the app, and send it the tutorial traffic once to check it works. Then stop the app and leave Postgres running.

What the agent does​

This chapter uses no skill. The agent reads the app's README and follows it:

  • Clones mock-lab and reads tutorial/<language>/README.md and tutorial/compose.yaml.
  • Checks that Docker is running and that ports 5432 and 8080 are free. If Docker Desktop is stopped, it starts it.
  • Runs docker compose up -d --wait from tutorial/. Postgres 16 starts on port 5432 with the schema from contract/schema.sql.
  • Builds and starts the app on port 8080, then runs the language's traffic driver, which sends 135 requests: health checks, catalog lookups, 40 orders with their reads, order lists, and a few bad requests that expect 400, 404 and 422.
  • Stops the app and leaves Postgres running for the next chapters.

What you should see​

The agent's summary. Trimmed:

The Go tutorial app works: the tutorial traffic sent 135 requests and got 0 unexpected responses. The app is now stopped and Postgres is still running.

- Postgres: I ran `docker compose up -d --wait` from `tutorial/`. The container `tutorial-postgres-1` (image `postgres:16`) is healthy on the default port 5432 ...
- App: ... It logged `tutorial-orders (go) listening on :8080 version=v1 slow=false`, and `/healthz` answered.
- Traffic: `go run ./cmd/traffic` printed `sent 135 requests, 0 unexpected`. The `orders` table now holds 40 rows. ...
- Stopped the app: I killed the process, and nothing is listening on port 8080 now.

The line that matters is sent 135 requests, 0 unexpected. The traffic driver prints one line for each response with an unexpected status.

If it goes wrong​

  • Docker is not running. Start Docker Desktop, or ask the agent to start it, and run the prompt again.
  • Port 5432 is already in use. Set TUTORIAL_DB_PORT to a free port before docker compose up -d, and point DATABASE_URL at that port, for example postgres://tutorial:tutorial@localhost:5433/tutorial?sslmode=disable. In later chapters, use the same port wherever a command maps to localhost:5432.
Manual equivalent
git clone https://github.com/speedscale/mock-lab
cd mock-lab/tutorial
docker compose up -d --wait

Then run the app and, in a second terminal, the traffic driver:

cd go
go run .                 # terminal 1
go run ./cmd/traffic     # terminal 2

Stop the app with ctrl-c and leave Postgres running.

Next​

Chapter 3: Record traffic