test: option to run a subset of tests

With this option, tests can be divided in groups and only one is run
from each group. This enables us to parallelize the tests across
multiple machines.

PR-URL: https://github.com/nodejs/io.js/pull/2260
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Alexis Campailla <alexis@janeasystems.com>

tools/test.py

@@ -1272,6 +1272,9 @@ def BuildOptions():
   result.add_option("--no-store-unexpected-output",
       help="Deletes the temporary JS files from tests that fails",
       dest="store_unexpected_output", action="store_false")
+  result.add_option("-r", "--run",
+      help="Divide the tests in m groups (interleaved) and run tests from group n (--run=n,m with n < m)",
+      default="")
   return result
 
 
@@ -1280,6 +1283,24 @@ def ProcessOptions(options):
   VERBOSE = options.verbose
   options.arch = options.arch.split(',')
   options.mode = options.mode.split(',')
+  options.run = options.run.split(',')
+  if options.run == [""]:
+    options.run = None
+  elif len(options.run) != 2:
+    print "The run argument must be two comma-separated integers."
+    return False
+  else:
+    try:
+      options.run = map(int, options.run)
+    except ValueError:
+      print "Could not parse the integers from the run argument."
+      return False
+    if options.run[0] < 0 or options.run[1] < 0:
+      print "The run argument cannot have negative integers."
+      return False
+    if options.run[0] >= options.run[1]:
+      print "The test group to run (n) must be smaller than number of groups (m)."
+      return False
   if options.J:
     options.j = multiprocessing.cpu_count()
   return True
@@ -1486,6 +1507,15 @@ def Main():
   def DoSkip(case):
     return SKIP in case.outcomes or SLOW in case.outcomes
   cases_to_run = [ c for c in all_cases if not DoSkip(c) ]
+  if options.run is not None:
+    # Must ensure the list of tests is sorted before selecting, to avoid
+    # silent errors if this file is changed to list the tests in a way that
+    # can be different in different machines
+    cases_to_run.sort(key=lambda c: (c.case.arch, c.case.mode, c.case.file))
+    cases_to_run = [ cases_to_run[i] for i
+                     in xrange(options.run[0],
+                               len(cases_to_run),
+                               options.run[1]) ]
   if len(cases_to_run) == 0:
     print "No tests to run."
     return 1