Improve reproducibility of test runs.

tools/run-tests.py

 #!/usr/bin/env python
 #
 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 16 matching lines @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
 import itertools
 import multiprocessing
 import optparse
 import os
 from os.path import join
 import platform
+import random
 import shlex
 import subprocess
 import sys
 import time
 
 from testrunner.local import execution
 from testrunner.local import progress
 from testrunner.local import testsuite
 from testrunner.local import utils
 from testrunner.local import verbose
@@ skipping 146 matching lines @@
   result.add_option("-v", "--verbose", help="Verbose output",
                     default=False, action="store_true")
   result.add_option("--valgrind", help="Run tests through valgrind",
                     default=False, action="store_true")
   result.add_option("--warn-unused", help="Report unused rules",
                     default=False, action="store_true")
   result.add_option("--junitout", help="File name of the JUnit output")
   result.add_option("--junittestsuite",
                     help="The testsuite name in the JUnit output file",
                     default="v8tests")
+  result.add_option("--random-seed", default=0, dest="random_seed",
+                    help="Default seed for initializing random generator")
   return result
 
 
 def ProcessOptions(options):
   global VARIANT_FLAGS
   global VARIANTS
 
   # Architecture and mode related stuff.
   if options.arch_and_mode:
     options.arch_and_mode = [arch_and_mode.split(".")
@@ skipping 30 matching lines @@
     options.no_network = True
   options.command_prefix = shlex.split(options.command_prefix)
   options.extra_flags = shlex.split(options.extra_flags)
 
   if options.gc_stress:
     options.extra_flags += GC_STRESS_FLAGS
 
   if options.j == 0:
     options.j = multiprocessing.cpu_count()
 
+  while options.random_seed == 0:
+    options.random_seed = random.SystemRandom().randint(-2147483648, 2147483647)
+
   def excl(*args):
     """Returns true if zero or one of multiple arguments are true."""
     return reduce(lambda x, y: x + y, args) <= 1
 
   if not excl(options.no_stress, options.stress_only, options.no_variants,
               bool(options.variants), options.quickcheck):
     print("Use only one of --no-stress, --stress-only, --no-variants, "
           "--variants, or --quickcheck.")
     return False
   if options.no_stress:
@@ skipping 126 matching lines @@
       timeout = 2 * TIMEOUT_DEFAULT;
     else:
       timeout = TIMEOUT_DEFAULT;
 
   timeout *= TIMEOUT_SCALEFACTOR[mode]
   ctx = context.Context(arch, mode, shell_dir,
                         mode_flags, options.verbose,
                         timeout, options.isolates,
                         options.command_prefix,
                         options.extra_flags,
-                        options.no_i18n)
+                        options.no_i18n,
+                        options.random_seed)
 
   # TODO(all): Combine "simulator" and "simulator_run".
   simulator_run = not options.dont_skip_simulator_slow_tests and \
       arch in ['arm64', 'arm', 'mips'] and ARCH_GUESS and arch != ARCH_GUESS
   # Find available test suites and read test cases from them.
   variables = {
     "arch": arch,
     "asan": options.asan,
     "deopt_fuzzer": False,
     "gc_stress": options.gc_stress,
@@ skipping 79 matching lines @@
   except KeyboardInterrupt:
     raise
 
   if options.time:
     verbose.PrintTestDurations(suites, overall_duration)
   return exit_code
 
 
 if __name__ == "__main__":
   sys.exit(Main())