Revert "Merge pull request #24046 from lidizheng/disable-exit-tests"

This reverts commit b78bc85185, reversing
changes made to 7c098321bd.

src/python/grpcio_tests/tests/unit/_exit_test.py

@@ -83,9 +83,6 @@ def wait(process):
     _process_wait_with_timeout(process)
 
 
-# TODO(lidiz) enable exit tests once the root cause found.
-@unittest.skip('https://github.com/grpc/grpc/issues/23982')
-@unittest.skip('https://github.com/grpc/grpc/issues/23028')
 class ExitTest(unittest.TestCase):
 
     def test_unstarted_server(self):
@@ -171,6 +168,7 @@ class ExitTest(unittest.TestCase):
             stderr=sys.stderr)
         interrupt_and_wait(process)
 
+    @unittest.skip('https://github.com/grpc/grpc/issues/23982')
     @unittest.skipIf(os.name == 'nt',
                      'os.kill does not have required permission on Windows')
     def test_in_flight_stream_stream_call(self):
@@ -200,6 +198,7 @@ class ExitTest(unittest.TestCase):
             stderr=sys.stderr)
         interrupt_and_wait(process)
 
+    @unittest.skip('https://github.com/grpc/grpc/issues/23982')
     @unittest.skipIf(os.name == 'nt',
                      'os.kill does not have required permission on Windows')
     def test_in_flight_partial_stream_stream_call(self):