Update L0 unit test script

tests/L0/run_test.py

+"""
 import unittest
 import sys
 
@@ -28,3 +29,79 @@ for test_dir in test_dirs:
         errcode = 1
 
 sys.exit(errcode)
+
+
+"""
+############################################################
+"""L0 Tests Runner.
+
+How to run this script?
+
+1. Run all the tests: `python /path/to/apex/tests/L0/run_test.py`
+2. Run one of the tests (e.g. fused layer norm):
+    `python /path/to/apex/tests/L0/run_test.py --include run_fused_layer_norm`
+3. Run two or more of the tests (e.g. optimizers and fused layer norm):
+    `python /path/to/apex/tests/L0/run_test.py --include run_optimizers run_fused_layer_norm`
+"""
+import argparse
+import os
+import unittest
+import sys
+
+from apex.testing.common_utils import TEST_WITH_ROCM
+from apex.testing.common_utils import SKIP_FLAKY_TEST
+
+TEST_ROOT = os.path.dirname(os.path.abspath(__file__))
+TEST_DIRS = [
+    "run_amp",
+    "run_fp16util",
+    "run_optimizers",
+    "run_fused_layer_norm",
+    "run_mlp",
+    "run_transformer",       # not fully supported on ROCm
+]
+DEFAULT_TEST_DIRS = [
+    "run_amp",
+    "run_fp16util",
+    "run_optimizers",
+    "run_fused_layer_norm",
+    "run_mlp",
+]
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+        description="L0 test runner",
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+    )
+    parser.add_argument(
+        "--include",
+        nargs="+",
+        choices=TEST_DIRS,
+        default=DEFAULT_TEST_DIRS,
+        help="select a set of tests to run (defaults to ALL tests).",
+    )
+    args, _ = parser.parse_known_args()
+    return args
+
+
+def main(args):
+    runner = unittest.TextTestRunner(verbosity=2)
+    errcode = 0
+    for test_dir in args.include:
+        test_dir = os.path.join(TEST_ROOT, test_dir)
+        print(test_dir)
+        suite = unittest.TestLoader().discover(test_dir)
+
+        print("\nExecuting tests from " + test_dir)
+        result = runner.run(suite)
+        if not result.wasSuccessful():
+            errcode = 1
+
+    sys.exit(errcode)
+
+
+if __name__ == '__main__':
+    args = parse_args()
+    main(args)
+