diff -r 5d43154d68a8 Lib/test/__main__.py
--- a/Lib/test/__main__.py	Sun Jul 08 21:03:01 2012 +0200
+++ b/Lib/test/__main__.py	Sun Jul 08 22:32:47 2012 -0700
@@ -1,13 +1,3 @@
-from test import regrtest, support
+from test import regrtest
 
-
-TEMPDIR, TESTCWD = regrtest._make_temp_dir_for_build(regrtest.TEMPDIR)
-regrtest.TEMPDIR = TEMPDIR
-regrtest.TESTCWD = TESTCWD
-
-# Run the tests in a context manager that temporary changes the CWD to a
-# temporary and writable directory. If it's not possible to create or
-# change the CWD, the original CWD will be used. The original CWD is
-# available from support.SAVEDCWD.
-with support.temp_cwd(TESTCWD, quiet=True):
-    regrtest.main()
+regrtest.main_with_temp_cwd()
diff -r 5d43154d68a8 Lib/test/regrtest.py
--- a/Lib/test/regrtest.py	Sun Jul 08 21:03:01 2012 +0200
+++ b/Lib/test/regrtest.py	Sun Jul 08 22:32:47 2012 -0700
@@ -229,6 +229,10 @@
         newsoft = min(hard, max(soft, 1024*2048))
         resource.setrlimit(resource.RLIMIT_STACK, (newsoft, hard))
 
+# A command option used internally to ensure that temp_cwd directories are
+# created in the same build folder when tests are run in multiprocess mode.
+_OPTION_CWD_PARENT_DIR = 'cwdparentdir'
+
 # Test result constants.
 PASSED = 1
 FAILED = 0
@@ -250,6 +254,72 @@
     print("Use --help for usage", file=sys.stderr)
     sys.exit(2)
 
+def parse_cwd_parent_dir_option():
+    """Preparse args, and return the --cwdparentdir option value.
+
+    Returns None on error or if not specified.
+
+    """
+    try:
+        opts, args = parse_args()
+    except Exception as err:
+        return
+    for opt, val in opts:
+        if opt == '--' + _OPTION_CWD_PARENT_DIR:
+            return val
+    return
+
+def parse_args():
+    opts, args = getopt.getopt(sys.argv[1:], 'hvqxsoS:rf:lu:t:TD:NLR:FdwWM:nj:Gm:',
+        ['help', 'verbose', 'verbose2', 'verbose3', 'quiet',
+         'exclude', 'single', 'slow', 'random', 'fromfile', 'findleaks',
+         'use=', 'threshold=', 'coverdir=', 'nocoverdir',
+         'runleaks', 'huntrleaks=', 'memlimit=', 'randseed=',
+         'multiprocess=', 'coverage', 'slaveargs=', 'forever', 'debug',
+         'start=', 'nowindows', 'header', 'testdir=', 'timeout=', 'wait',
+         'failfast', 'match', _OPTION_CWD_PARENT_DIR + '='])
+    return opts, args
+
+def _make_temp_dir_for_build():
+    """Create and return a build directory.
+
+    """
+    temp_dir = os.path.join(sysconfig.get_config_var('srcdir'), 'build')
+    temp_dir = os.path.abspath(temp_dir)
+    try:
+        os.mkdir(temp_dir)
+    except FileExistsError:
+        pass
+    return temp_dir
+
+def main_with_temp_cwd(cwd_parent_dir=None):
+    """Execute a test suite in a temporary working directory.
+
+    """
+    global TEMPDIR, TESTCWD
+
+    if cwd_parent_dir is None:
+        # When tests are run from the Python build directory, it is best
+        # practice to keep the test files in a subfolder.  This simplifies
+        # the cleanup of leftover files using command "make distclean".
+        if sysconfig.is_python_build():
+            TEMPDIR = _make_temp_dir_for_build()
+    else:
+        TEMPDIR = cwd_parent_dir
+
+    # Define a writable temp dir that will be used as cwd while running
+    # the tests. The name of the dir includes the pid to allow parallel
+    # testing (see the -j option).
+    TESTCWD = 'test_python_{}'.format(os.getpid())
+
+    TESTCWD = os.path.join(TEMPDIR, TESTCWD)
+
+    # Run the tests in a context manager that temporarily changes the CWD to
+    # a temporary and writable directory. If it's not possible to create or
+    # change the CWD, the original CWD will be used. The original CWD is
+    # available from support.SAVEDCWD.
+    with support.temp_cwd(TESTCWD, quiet=True):
+        main()
 
 def main(tests=None, testdir=None, verbose=0, quiet=False,
          exclude=False, single=False, randomize=False, fromfile=None,
@@ -296,14 +366,7 @@
 
     support.record_original_stdout(sys.stdout)
     try:
-        opts, args = getopt.getopt(sys.argv[1:], 'hvqxsoS:rf:lu:t:TD:NLR:FdwWM:nj:Gm:',
-            ['help', 'verbose', 'verbose2', 'verbose3', 'quiet',
-             'exclude', 'single', 'slow', 'random', 'fromfile', 'findleaks',
-             'use=', 'threshold=', 'coverdir=', 'nocoverdir',
-             'runleaks', 'huntrleaks=', 'memlimit=', 'randseed=',
-             'multiprocess=', 'coverage', 'slaveargs=', 'forever', 'debug',
-             'start=', 'nowindows', 'header', 'testdir=', 'timeout=', 'wait',
-             'failfast', 'match'])
+        opts, args = parse_args()
     except getopt.error as msg:
         usage(msg)
 
@@ -443,6 +506,9 @@
             print()   # Force a newline (just in case)
             print(json.dumps(result))
             sys.exit(0)
+        elif o == '--' + _OPTION_CWD_PARENT_DIR:
+            # This option is incorporated prior to calling main().
+            pass
         elif o == '--testdir':
             # CWD is replaced with a temporary dir before calling main(), so we
             # join it with the saved CWD so it ends up where the user expects.
@@ -623,7 +689,8 @@
                 yield (test, args_tuple)
         pending = tests_and_args()
         opt_args = support.args_from_interpreter_flags()
-        base_cmd = [sys.executable] + opt_args + ['-m', 'test.regrtest']
+        base_cmd = ([sys.executable] + opt_args +
+                    ['-m', 'test.regrtest', '--' + _OPTION_CWD_PARENT_DIR, TEMPDIR])
         def work():
             # A worker thread.
             try:
@@ -1735,26 +1802,6 @@
         assert self.isvalid()
         return self.expected
 
-def _make_temp_dir_for_build(TEMPDIR):
-    # When tests are run from the Python build directory, it is best practice
-    # to keep the test files in a subfolder.  It eases the cleanup of leftover
-    # files using command "make distclean".
-    if sysconfig.is_python_build():
-        TEMPDIR = os.path.join(sysconfig.get_config_var('srcdir'), 'build')
-        TEMPDIR = os.path.abspath(TEMPDIR)
-        try:
-            os.mkdir(TEMPDIR)
-        except FileExistsError:
-            pass
-
-    # Define a writable temp dir that will be used as cwd while running
-    # the tests. The name of the dir includes the pid to allow parallel
-    # testing (see the -j option).
-    TESTCWD = 'test_python_{}'.format(os.getpid())
-
-    TESTCWD = os.path.join(TEMPDIR, TESTCWD)
-    return TEMPDIR, TESTCWD
-
 if __name__ == '__main__':
     # Remove regrtest.py's own directory from the module search path. Despite
     # the elimination of implicit relative imports, this is still needed to
@@ -1777,11 +1824,6 @@
     # sanity check
     assert __file__ == os.path.abspath(sys.argv[0])
 
-    TEMPDIR, TESTCWD = _make_temp_dir_for_build(TEMPDIR)
+    cwd_parent_dir = parse_cwd_parent_dir_option()
 
-    # Run the tests in a context manager that temporary changes the CWD to a
-    # temporary and writable directory. If it's not possible to create or
-    # change the CWD, the original CWD will be used. The original CWD is
-    # available from support.SAVEDCWD.
-    with support.temp_cwd(TESTCWD, quiet=True):
-        main()
+    main_with_temp_cwd(cwd_parent_dir=cwd_parent_dir)
diff -r 5d43154d68a8 Misc/ACKS
--- a/Misc/ACKS	Sun Jul 08 21:03:01 2012 +0200
+++ b/Misc/ACKS	Sun Jul 08 22:32:47 2012 -0700
@@ -505,6 +505,7 @@
 Drew Jenkins
 Flemming Kjær Jensen
 MunSic Jeong
+Chris Jerdonek
 Jim Jewett
 Orjan Johansen
 Fredrik Johansson
diff -r 5d43154d68a8 Misc/NEWS
--- a/Misc/NEWS	Sun Jul 08 21:03:01 2012 +0200
+++ b/Misc/NEWS	Sun Jul 08 22:32:47 2012 -0700
@@ -104,6 +104,9 @@
 - Issue #15284: Skip {send,recv}msg tests in test_socket when IPv6 is not
   enabled. Patch by Brian Brazil.
 
+- Issue #15300: Ensure the temporary test working directories are in the same
+  folder when running tests in multiprocess mode. Patch by Chris Jerdonek.
+
 - Issue #15277: Fix a resource leak in support.py when IPv6 is disabled.
   Patch by Brian Brazil.