Add --test-files option to py.test

At this point, py.test should be equivalent to test/run.py

test/conftest.py

@@ -8,18 +8,40 @@ def pytest_addoption(parser):
     parser.addoption(
         "--base-dir", default=default_base_dir,
         help="Directory in which integration test case files locate.")
+    parser.addoption(
+        "--test-files", "-T", default=[], action='append',
+        help=(
+            "Specify test files using FILE_NAME[:LINE[,LINE[,...]]]. "
+            "For example: -T generators.py:10,13,19. "
+            "Note that you can use -m to specify the test case by id."))
     parser.addoption(
         "--thirdparty",
         help="Include integration tests that requires third party modules.")
 
 
+def parse_test_files_option(opt):
+    """
+    Parse option passed to --test-files into a key-value pair.
+
+    >>> parse_test_files_option('generators.py:10,13,19')
+    ('generators.py', [10, 13, 19])
+    """
+    opt = str(opt)
+    if ':' in opt:
+        (f_name, rest) = opt.split(':', 1)
+        return (f_name, list(map(int, rest.split(','))))
+    else:
+        return (opt, [])
+
+
 def pytest_generate_tests(metafunc):
     """
     :type metafunc: _pytest.python.Metafunc
     """
     if 'case' in metafunc.fixturenames:
         base_dir = metafunc.config.option.base_dir
-        test_files = {}
+        test_files = dict(map(parse_test_files_option,
+                              metafunc.config.option.test_files))
         thirdparty = metafunc.config.option.thirdparty
         metafunc.parametrize(
             'case',