api-test resolves ${VAR} and ${VAR:-default} placeholders in its
YAML config at load time. Plain $VAR (no braces) is left untouched
so Postgres DSN-style strings don't get rewritten.
This page documents the conventional APITEST_* variables the shipped
configs expect.
${APITEST_DEV_KEY:-devkey-please-change} resolves to the env var
when set, else to the literal default. Use the default form for
fixtures that should "just work" out of the box; use the bare
${APITEST_DEV_KEY} form for required values where missing should
fail loudly.