This make it possible to easily run individual guru tests.
It also slightly speeds up the overall test run,
from 23s to 18s on my machine;
the TestGuru/calls is now the limiting factor,
by a significant margin.
This work supported by Sourcegraph.
Change-Id: If61ebf1cc60441a65274f3fddd31f69c7ca23b48
Reviewed-on: https://go-review.googlesource.com/108876
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>