gh-140082: Forward colorizing from libregrtest to unittest

libregrtest redirects test output to a file as part of its operation.
When `unittest` checks to see if it should colorize with
`isatty(sys.stdout)` that fails resulting in no colorizing of the
unittest output.

Update `libregrtest` to set `FORCE_COLOR=1` when redirecting test output
so that unittest will do color printing.

Author: cmaloney

Lib/test/libregrtest/single.py

@@ -2,12 +2,13 @@
 import gc
 import importlib
 import io
+import os
 import sys
 import time
 import traceback
 import unittest
 
-from _colorize import get_colors  # type: ignore[import-not-found]
+from _colorize import can_colorize, get_colors  # type: ignore[import-not-found]
 from test import support
 from test.support import threading_helper
 
@@ -274,6 +275,9 @@ def _runtest(result: TestResult, runtests: RunTests) -> None:
     output_on_failure = runtests.output_on_failure
     timeout = runtests.timeout
 
+    if can_colorize(file=sys.stdout):
+        os.environ['FORCE_COLOR'] = "1"
+
     if timeout is not None and threading_helper.can_start_thread:
         use_timeout = True
         faulthandler.dump_traceback_later(timeout, exit=True)

Lib/test/libregrtest/worker.py

@@ -1,3 +1,4 @@
+import _colorize
 import subprocess
 import sys
 import os
@@ -32,6 +33,12 @@ def create_worker_process(runtests: WorkerRunTests, output_fd: int,
         env['TEMP'] = tmp_dir
         env['TMP'] = tmp_dir
 
+    # The subcommand is run with a temporary output which means it is not a tty
+    # and won't auto-color. The test results are printed to stdout so if we can
+    # color that have the subprocess use color.
+    if _colorize.can_colorize(file=sys.stdout):
+        env['FORCE_COLOR'] = '1'
+
     # Running the child from the same working directory as regrtest's original
     # invocation ensures that TEMPDIR for the child is the same when
     # sysconfig.is_python_build() is true. See issue 15300.