String "eternal", "long", "moderate", or "short"
with the default derived from a test's size attribute)
How long the test is normally expected to run before returning.
While a test's size attribute controls resource estimation, a test's timeout may be set independently. If not explicitly specified, the timeout is based on the test's size (with "small" ⇒ "short", "medium" ⇒ "moderate", etc...). By default, "short" means 1 minute, "moderate" 5 minutes, and "long" 15 minutes (this can be overridden with --test_timeout, e.g. for running under certain configurations which are known to be slow).