Auto merge of #18984 - dsandeephegde:master, r=jdm

 Initial steps of Mutation testing

<!-- Please describe your changes on the following line: -->
- Added one strategy of mutation which is replacing occurrences && to ||.
- Added test mapping framework for running mutation tests corresponding to a mutant.
- Added one test_mapping.json to map source file in a folder to WPT test.
- Added README mentioning about Mutation testing.
- Added CI script to invoke mutation test.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes #18529 (github issue number if applicable).
- [x] These changes do not require tests because it is a python script to run mutation test and does not change any behavior.

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1 files changed, 78 insertions, 0 deletions

diff --git a/python/servo/mutation/test.py b/python/servo/mutation/test.py
new file mode 100644
index 00000000000..2248f81ccd3
--- /dev/null
+++ b/python/servo/mutation/test.py
@@ -0,0 +1,78 @@
+# Copyright 2013 The Servo Project Developers. See the COPYRIGHT
+# file at the top-level directory of this distribution.
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+import fileinput
+import re
+import subprocess
+import sys
+import os
+import random
+from enum import Enum
+DEVNULL = open(os.devnull, 'wb')
+
+
+class Status(Enum):
+    KILLED = 0
+    SURVIVED = 1
+    SKIPPED = 2
+    UNEXPECTED = 3
+
+
+def mutate_random_line(file_name, strategy):
+    line_numbers = []
+    for line in fileinput.input(file_name):
+        if re.search(strategy['regex'], line):
+            line_numbers.append(fileinput.lineno())
+    if len(line_numbers) == 0:
+        return -1
+    else:
+        mutation_line_number = line_numbers[random.randint(0, len(line_numbers) - 1)]
+        for line in fileinput.input(file_name, inplace=True):
+            if fileinput.lineno() == mutation_line_number:
+                line = re.sub(strategy['regex'], strategy['replaceString'], line)
+            print line.rstrip()
+        return mutation_line_number
+
+
+def mutation_test(file_name, tests):
+    status = Status.UNEXPECTED
+    local_changes_present = subprocess.call('git diff --quiet {0}'.format(file_name), shell=True)
+    if local_changes_present == 1:
+        status = Status.SKIPPED
+        print "{0} has local changes, please commit/remove changes before running the test".format(file_name)
+    else:
+        strategy = {'regex': r'\s&&\s', 'replaceString': ' || '}
+        mutated_line = mutate_random_line(file_name, strategy)
+        if mutated_line != -1:
+            print "Mutating {0} at line {1}".format(file_name, mutated_line)
+            print "compiling mutant {0}:{1}".format(file_name, mutated_line)
+            sys.stdout.flush()
+            subprocess.call('python mach build --release', shell=True, stdout=DEVNULL)
+            for test in tests:
+                test_command = "python mach test-wpt {0} --release".format(test.encode('utf-8'))
+                print "running `{0}` test for mutant {1}:{2}".format(test, file_name, mutated_line)
+                sys.stdout.flush()
+                test_status = subprocess.call(test_command, shell=True, stdout=DEVNULL)
+                if test_status != 0:
+                    print("Failed: while running `{0}`".format(test_command))
+                    print "mutated file {0} diff".format(file_name)
+                    sys.stdout.flush()
+                    subprocess.call('git --no-pager diff {0}'.format(file_name), shell=True)
+                    status = Status.SURVIVED
+                else:
+                    print("Success: Mutation killed by {0}".format(test.encode('utf-8')))
+                    status = Status.KILLED
+                    break
+            print "reverting mutant {0}:{1}".format(file_name, mutated_line)
+            sys.stdout.flush()
+            subprocess.call('git checkout {0}'.format(file_name), shell=True)
+        else:
+            print "Cannot mutate {0}".format(file_name)
+        print "-" * 80 + "\n"
+    return status