Added update_test_expectations script to remove non-flaky test expectations.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
new file mode 100644
index 0000000000000000000000000000000000000000..775ea2f7dcdb5f000aeab790236c35731252219e
--- /dev/null
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
@@ -0,0 +1,217 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import argparse
+
+from webkitpy.layout_tests.port import builders
+from webkitpy.layout_tests.models.test_expectations import TestExpectations
+from webkitpy.layout_tests.layout_package.bot_test_expectations import BotTestExpectationsFactory
+
+
+def main(host, argv):
+    parser = argparse.ArgumentParser(epilog=("""
+        Scans the TestExpectations file
+        and uses results from actual builder bots runs to remove tests that are
+        marked as flaky but don't fail in the specified way.
+
+        E.g. If a test has this expectation:
+            bug(test) fast/test.html [ Failure Pass ]
+
+        And all the runs on builders have passed the line will be removed.
+
+        Additionally, the runs don't all have to be Passing to remove the line;
+        as long as the non-Passing results are of a type not specified in the
+        expectation this line will be removed. For example, if this is the
+        expectation:
+
+            bug(test) fast/test.html [ Crash Pass ]
+
+        But the results on the builders show only Passes and Timeouts, the line
+        will be removed since there's no Crash results.
+        """), formatter_class=argparse.RawTextHelpFormatter)

[Dirk Pranke, 2016/03/29 22:39:01]

I would actually move this string up to the top-level docstring (i.e., move it
after line 4), and then use epilog=__doc__).

[bokan, 2016/04/05 12:28:57]

Done.

+    args = parser.parse_args(argv)
+
+    port = host.port_factory.get()
+    bot_test_expectations_factory = BotTestExpectationsFactory()
+
+    remove_flakes_o_matic = RemoveFlakesOMatic(host,
+                                               port,
+                                               bot_test_expectations_factory)
+
+    test_expectations = remove_flakes_o_matic.get_updated_test_expectations()
+
+    if not test_expectations:
+        # TODO(bokan): How should we report errors?
+        return None
+
+    expectations_file = port.path_to_generic_test_expectations_file()
+
+    remove_flakes_o_matic.write_test_expectations(test_expectations,
+                                                  expectations_file)

[qyearsley, 2016/03/21 21:45:25]

Note, the unit test doesn't cover main(), or write_test_expectations(), but I
think that's fine assuming that it's manually tested by running the script.

[Dirk Pranke, 2016/03/29 22:39:01]

By passing a MockHost() to main, you can (and should) stub out everything
without actually incurring any file i/o, 
so you should be able to write tests for that as well.

You should probably add a method to MockHost() to return a faked-out
BotTestExpectationsFactory() so you
can control the output of that as well.

[bokan, 2016/04/05 12:28:56]

Added a TODO, will add shortly.

+
+
+class RemoveFlakesOMatic:

[Dirk Pranke, 2016/03/29 22:39:01]

derive this class from object, i.e. RemoveFlakesOMatic(object).

[bokan, 2016/04/05 12:28:56]

Done.

+    def __init__(self, host, port, bot_test_expectations_factory):
+        self._host = host
+        self._port = port
+        self._expectations_factory = bot_test_expectations_factory
+
+    def _can_delete_line(self, test_expectation_line):
+        """Returns whether a given line in the expectations can be removed.
+
+        Uses results from builder bots to determine if a given line is stale and
+        can safely be removed from the TestExpectations file. (i.e. remove if
+        the bots show that it's not flaky.) There's also some rules about when
+        not to remove lines (e.g. never remove lines with Rebaseline
+        expectations, don't remove non-flaky expectations, etc.)
+
+        Args:
+            test_expectation_line (TestExpectationLine): A line in the test
+                expectation file to test for possible removal.
+
+        Returns: True if the line can be removed, False otherwise.
+        """
+        expectations = test_expectation_line.expectations
+        if len(expectations) < 2:
+            return False
+
+        if self._has_unstrippable_expectations(expectations):
+            return False
+
+        if not self._has_pass_expectation(expectations):
+            return False
+
+        # The line can be deleted if the only expectation on the line that appears in the actual
+        # results is the PASS expectation.
+        for config in test_expectation_line.matching_configurations:
+            builder_name = builders.builder_name_for_specifiers(config.version, config.build_type)
+
+            if not builder_name:
+                # TODO(bokan): We probably want to report a problem if we can't
+                # turn the specifiers into a builder name.
+                # TODO(bokan): Matching configurations often give us bots that don't have a
+                # builder in builders.py's exact_matches. Should we ignore those or be conservative
+                # and assume we need these expectations to make a decision?

[Dirk Pranke, 2016/03/29 22:39:01]

Are you wondering about cases like Debug bots where we don't run the tests on
every o/s in debug?

[bokan, 2016/04/05 12:28:56]

Yah, I think it's mostly debug, but not all. The matching_configurations that
aren't in builders.py include:

    [icecreamsandwich, x86, release]

The Mac10.11 bot has this configuration:

    [mac10.11, x86, debug]

But builders.py's specifiers use "10.11" instead of "Mac10.11". Is it right to
be matching up the specifiers in builders.py to the ones in
matching_configurations?

+                return False
+
+            if builder_name not in self.builder_results_by_path.keys():
+                # TODO(bokan): We probably want to report a problem if we can't get results for
+                # a bot specified in expectatoins.
+                return False

[qyearsley, 2016/03/21 21:45:25]

For here and above, I agree that logging an error would be good.

It may also be a good idea to test the logging of these different kinds of error
in the unit test.

[bokan, 2016/04/05 12:28:56]

Added logging messages. Will add tests shortly.

+
+            results_by_path = self.builder_results_by_path[builder_name]
+
+            # No results means the test was all skipped or all results are passing.

[qyearsley, 2016/03/21 21:45:25]

test was all skipped -> tests were all skipped

[bokan, 2016/04/05 12:28:56]

Done.

+            if test_expectation_line.path not in results_by_path.keys():
+                continue

[qyearsley, 2016/03/21 21:45:25]

This line is not covered by the unit test right now; maybe we could add one test
method where all tests are pass/skip (and the test expectations are not
modified)?

[bokan, 2016/04/05 12:28:56]

Ack. Added a TODO, will do shortly.

+
+            results_for_single_test = results_by_path[test_expectation_line.path]
+
+            if self._expectations_that_were_met(test_expectation_line, results_for_single_test) != set(['PASS']):
+                return False
+
+        return True
+
+    def _has_pass_expectation(self, expectations):
+        return 'PASS' in expectations
+
+    def _expectations_that_were_met(self, test_expectation_line, results_for_single_test):
+        """Returns the set of expectations that appear in the given results.
+
+        e.g. If the test expectations is:
+            bug(test) fast/test.html [Crash Failure Pass]
+
+        And the results are ['TEXT', 'PASS', 'PASS', 'TIMEOUT']
+
+        This method would return [Pass Failure]
+
+        Args:
+            test_expectation_line: A TestExpectationLine object
+            results_for_single_test: A list of result strings.
+                e.g. ['IMAGE', 'IMAGE', 'PASS']
+
+        Returns:
+            A set containing expectations that occured in the results.
+        """
+        # TODO(bokan): Does this not exist in a more central place?
+        def replace_failing_with_fail(expectation):
+            if expectation in ('TEXT', 'IMAGE', 'IMAGE+TEXT', 'AUDIO'):
+                return 'FAIL'
+            else:
+                return expectation
+
+        actual_results = {replace_failing_with_fail(r) for r in results_for_single_test}
+
+        return set(test_expectation_line.expectations) & actual_results
+
+    def _has_unstrippable_expectations(self, expectations):
+        """ Returns whether any of the given expectations are considered unstrippable.
+
+        Unstrippable expectations are those which should stop a line from being
+        removed regardless of builder bot results.
+
+        Args:
+            expectations: A list of string expectations.
+                E.g. ['PASS', 'FAIL' 'CRASH']
+
+        Returns:
+            True if at least one of the expectations is unstrippable. False
+            otherwise.
+        """
+        unstrippable_expectations = ('REBASELINE', 'NEEDSREBASELINE',
+                                     'NEEDSMANUALREBASELINE', 'SLOW')
+        return any(s in expectations for s in unstrippable_expectations)
+
+    def get_updated_test_expectations(self):
+        test_expectations = TestExpectations(self._port, include_overrides=False).expectations()
+
+        self.builder_results_by_path = {}
+        for builder_name in builders.all_builder_names():
+            expectations_for_builder = (
+                self._expectations_factory.expectations_for_builder(builder_name)
+            )
+
+            # TODO(bokan): Error message?
+            if not expectations_for_builder:
+                return None

[qyearsley, 2016/03/21 21:45:25]

Logging an error here sounds good to me. Also, this line isn't currently covered
by the unit tests.

When will self._expectations_factory.expectations_for_builder(builder_name) be
None or empty?

[bokan, 2016/04/05 12:28:56]

Added log message. TODO and working on test.
It shouldn't happen normally, I think. If the results JSON doesn't include a
builder from builders.py. I'm not sure how the JSON is generated so I don't know
what happens if a bot goes down or we decomission one.

+
+            self.builder_results_by_path[builder_name] = (
+                expectations_for_builder.all_results_by_path()
+            )
+
+        expectations_to_remove = []
+
+        for expectation in test_expectations:
+            if self._can_delete_line(expectation):
+                expectations_to_remove.append(expectation)
+
+        for expectation in expectations_to_remove:
+            index = test_expectations.index(expectation)
+            test_expectations.remove(expectation)
+
+            # Remove associated comments and whitespace if we've removed the last expectation under
+            # a comment block. Only remove a comment block if it's not separated from the tests by
+            # whitespace.

[qyearsley, 2016/03/21 21:45:25]

Would it be correct to rephrase "if it's not separated by the tests by
whitespace" as "if it's not separated by the test expectation lines by a blank
line"?

[bokan, 2016/04/05 12:28:56]

Done. (replaced with "if it's not separated _from_ the test expectation line by
whitespace)

+            if index == len(test_expectations) or test_expectations[index].is_whitespace_or_comment():
+                removed_whitespace = False
+                while index and test_expectations[index - 1].is_whitespace():
+                    index = index - 1
+                    test_expectations.pop(index)
+                    removed_whitespace = True

[qyearsley, 2016/03/21 21:45:25]

I think there may be no test case that covers this while clause currently --
this should be covered as long as we have a test method where there's an example
test expectations with multiple blank lines in a row, right?

[bokan, 2016/04/05 12:28:56]

It should be covered by test_preserve_comments_and_whitespace

+
+                if not removed_whitespace:
+                    while index and test_expectations[index - 1].is_comment():
+                        index = index - 1
+                        test_expectations.pop(index)
+
+                    while index and test_expectations[index - 1].is_whitespace():
+                        index = index - 1
+                        test_expectations.pop(index)
+
+        return test_expectations
+
+    def write_test_expectations(self, test_expectations, test_expectations_file):
+        self._host.filesystem.write_text_file(
+            test_expectations_file,
+            TestExpectations.list_to_string(test_expectations, reconstitute_only_these=[]))