[githooks] Add a test runner

This CL adds a test-runner as ./run_tests_for.py. This can manually be
invoked pretty easily; just hand it a few files, and it'll try to figure
out what tests need to be run for that. If it finds any tests, they'll
be run in parallel.

This includes an incidental update to our yapf style, per reviewer
comments.

The intent is to use this script to run tests as part of a `repo upload`
hook.

Test discovery is kind of haphazard, and split into two phases.
Basically, there's a set of directories where if you touch anything in
that directory, all tests in that directory get run (see
`_find_forced_subdir_tests`). Otherwise, this script just tries to find
names of files similar to the ones it's given, but with _test/_unittest
in them.

I chose this method of discovery since `foo_unittest.py` and
`foo_test.py` appear to be the two prevalent naming conventions here,
and no one wants to keep a text file (or similar) up-to-date with all of
the tests that exist.

At the moment, this only supports Python. Adding support for
auto-detecting other tests should hopefully be straightforward enough,
if we want to add it.

BUG=None
TEST=Ran crosperf's tests. Observed failures.

Change-Id: Ieeb3e5ad25011c6ef2f93908b051c4da1e776350
Reviewed-on: https://chromium-review.googlesource.com/1516414
Commit-Ready: George Burgess <gbiv@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/.style.yapf b/.style.yapf
index de0c6a70..97f7d657 100644
--- a/.style.yapf
+++ b/.style.yapf
@@ -1,2 +1,3 @@
 [style]
 based_on_style = chromium
+blank_line_before_module_docstring = true