Note: since this edge lambda is manually deployed, these tests won't actually "validate" staging. So I'll probably do some manual intervention every time this deploys:
Something merges to dovetail-stitch-lambda master, deploys to staging
Tests run against the old version in staging
Manually update the CF distribution to point at new version of the lambda
Wait
Re-trigger the tests, to run against new version in staging, old version in production
Generate unique filenames, to make sure the stitch lambda is actually creating a new file on every request.