See testdata/README for test format.
This will make it easier to fix problems and not regress.
Markdown tests in followup CL (with bug fixes).
Change-Id: I5dedca26d3c29fd428066ffb38c6605343784a19
Reviewed-on: https://go-review.googlesource.com/c/tools/+/224957
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
