bpo-30540: regrtest: add --matchfile option (#1909)

* Add a new option taking a filename to get a list of test names to
  filter tests.
* support.match_tests becomes a list.
* Modify run_unittest() to accept to match the whole test identifier,
  not just a part of a test identifier.

For example, the following command only runs test_default_timeout()
of the BarrierTests class of test_threading:

$ ./python -m test -v test_threading -m test.test_threading.BarrierTests.test_default_timeout

Remove also some empty lines from test_regrtest.py to make flake8
tool happy.

Lib/test/test_regrtest.py

@@ -159,9 +159,24 @@ class ParseArgsTestCase(unittest.TestCase):
         for opt in '-m', '--match':
             with self.subTest(opt=opt):
                 ns = libregrtest._parse_args([opt, 'pattern'])
-                self.assertEqual(ns.match_tests, 'pattern')
+                self.assertEqual(ns.match_tests, ['pattern'])
                 self.checkError([opt], 'expected one argument')
 
+        ns = libregrtest._parse_args(['-m', 'pattern1',
+                                      '-m', 'pattern2'])
+        self.assertEqual(ns.match_tests, ['pattern1', 'pattern2'])
+
+        self.addCleanup(support.unlink, support.TESTFN)
+        with open(support.TESTFN, "w") as fp:
+            print('matchfile1', file=fp)
+            print('matchfile2', file=fp)
+
+        filename = os.path.abspath(support.TESTFN)
+        ns = libregrtest._parse_args(['-m', 'match',
+                                      '--matchfile', filename])
+        self.assertEqual(ns.match_tests,
+                         ['match', 'matchfile1', 'matchfile2'])
+
     def test_failfast(self):
         for opt in '-G', '--failfast':
             with self.subTest(opt=opt):
@@ -275,7 +290,6 @@ class ParseArgsTestCase(unittest.TestCase):
                 ns = libregrtest._parse_args([opt])
                 self.assertTrue(ns.forever)
 
-
     def test_unrecognized_argument(self):
         self.checkError(['--xxx'], 'usage:')
 
@@ -457,7 +471,6 @@ class BaseTestCase(unittest.TestCase):
             self.fail(msg)
         return proc
 
-
     def run_python(self, args, **kw):
         args = [sys.executable, '-X', 'faulthandler', '-I', *args]
         proc = self.run_command(args, **kw)
@@ -823,6 +836,52 @@ class ArgsTestCase(BaseTestCase):
         self.check_executed_tests(output, tests, failed=crash_test,
                                   randomize=True)
 
+    def parse_methods(self, output):
+        regex = re.compile("^(test[^ ]+).*ok$", flags=re.MULTILINE)
+        return [match.group(1) for match in regex.finditer(output)]
+
+    def test_matchfile(self):
+        # Any code which causes a crash
+        code = textwrap.dedent("""
+            import unittest
+
+            class Tests(unittest.TestCase):
+                def test_method1(self):
+                    pass
+                def test_method2(self):
+                    pass
+                def test_method3(self):
+                    pass
+                def test_method4(self):
+                    pass
+        """)
+        all_methods = ['test_method1', 'test_method2',
+                       'test_method3', 'test_method4']
+        testname = self.create_test(code=code)
+
+        # by default, all methods should be run
+        output = self.run_tests("-v", testname)
+        methods = self.parse_methods(output)
+        self.assertEqual(methods, all_methods)
+
+        # only run a subset
+        filename = support.TESTFN
+        self.addCleanup(support.unlink, filename)
+
+        subset = [
+            # only match the method name
+            'test_method1',
+            # match the full identifier
+            '%s.Tests.test_method3' % testname]
+        with open(filename, "w") as fp:
+            for name in subset:
+                print(name, file=fp)
+
+        output = self.run_tests("-v", "--matchfile", filename, testname)
+        methods = self.parse_methods(output)
+        subset = ['test_method1', 'test_method3']
+        self.assertEqual(methods, subset)
+
 
 if __name__ == '__main__':
     unittest.main()