Update docs for runtime enabled features and web tests
Change-Id: I7230bd37e7f9c1c136e1c23b6acdc340eb089121
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303452
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789247}
diff --git a/docs/testing/web_tests.md b/docs/testing/web_tests.md
index faa428c..3396360 100644
--- a/docs/testing/web_tests.md
+++ b/docs/testing/web_tests.md
@@ -217,7 +217,7 @@
There are two ways to run web tests with additional command-line arguments:
-* Using `--additional-driver-flag`:
+* Using `--additional-driver-flag` or `--flag-specific`:
```bash
third_party/blink/tools/run_web_tests.py --additional-driver-flag=--blocking-repaint
@@ -300,8 +300,15 @@
with the flags without creating any virtual tests.
For flags whose implementation is still in progress, virtual test suites and
-flag-specific expectations represent two alternative strategies for testing.
-Consider the following when choosing between them:
+flag-specific expectations represent two alternative strategies for testing both
+the enabled code path and not-enabled code path. They are preferred to only
+setting a [runtime enabled feature](../../third_party/blink/renderer/platform/RuntimeEnabledFeatures.md)
+to `status: "test"` if the feature has substantially different code path from
+production because the latter would cause loss of test coverage of the production
+code path.
+
+Consider the following when choosing between virtual test suites and
+flag-specific expectations:
* The
[waterfall builders](https://dev.chromium.org/developers/testing/chromium-build-infrastructure/tour-of-the-chromium-buildbot)
@@ -309,7 +316,8 @@
will run all virtual test suites in addition to the non-virtual tests.
Conversely, a flag-specific expectations file won't automatically cause the
bots to test your flag - if you want bot coverage without virtual test suites,
- you will need to set up a dedicated bot for your flag.
+ you will need to set up a dedicated bot ([example](https://chromium-review.googlesource.com/c/chromium/src/+/1850255))
+ for your flag.
* Due to the above, virtual test suites incur a performance penalty for the
commit queue and the continuous build infrastructure. This is exacerbated by
