Add a unit test to verify controller objects do not persist across classes. (#483)

In the same run (calling `TestRunner.run` once) with multiple test classes,
the controller objects should be recreated for each class and not be reused.
diff --git a/tests/mobly/test_suite_test.py b/tests/mobly/test_suite_test.py
new file mode 100755
index 0000000..7e15f25
--- /dev/null
+++ b/tests/mobly/test_suite_test.py
@@ -0,0 +1,85 @@
+# Copyright 2018 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import mock
+import shutil
+import tempfile
+
+from future.tests.base import unittest
+
+from mobly import base_test
+from mobly import config_parser
+from mobly import records
+from mobly import test_runner
+
+from tests.lib import mock_controller
+from tests.lib import utils
+
+
+class TestSuiteTest(unittest.TestCase):
+    """Tests for use cases of creating Mobly test suites.
+
+    Tests here target a combination of test_runner and base_test code.
+    """
+
+    def setUp(self):
+        self.tmp_dir = tempfile.mkdtemp()
+        self.mock_test_cls_configs = config_parser.TestRunConfig()
+        self.summary_file = os.path.join(self.tmp_dir, 'summary.yaml')
+        self.mock_test_cls_configs.summary_writer = records.TestSummaryWriter(
+            self.summary_file)
+        self.mock_test_cls_configs.log_path = self.tmp_dir
+        self.mock_test_cls_configs.user_params = {"some_param": "hahaha"}
+        self.mock_test_cls_configs.reporter = mock.MagicMock()
+        self.base_mock_test_config = config_parser.TestRunConfig()
+        self.base_mock_test_config.test_bed_name = 'SampleTestBed'
+        self.base_mock_test_config.controller_configs = {}
+        self.base_mock_test_config.user_params = {
+            'icecream': 42,
+            'extra_param': 'haha'
+        }
+        self.base_mock_test_config.log_path = self.tmp_dir
+
+    def tearDown(self):
+        shutil.rmtree(self.tmp_dir)
+
+    def test_controller_object_not_persistent_across_classes_in_the_same_run(
+            self):
+        self.foo_test_controller_obj_id = None
+        self.bar_test_controller_obj_id = None
+        test_run_config = self.base_mock_test_config.copy()
+        test_run_config.controller_configs = {'MagicDevice': [{'serial': 1}]}
+
+        class FooTest(base_test.BaseTestClass):
+            def setup_class(cls):
+                cls.controller = cls.register_controller(mock_controller)[0]
+                self.foo_test_controller_obj_id = id(cls.controller)
+
+        class BarTest(base_test.BaseTestClass):
+            def setup_class(cls):
+                cls.controller = cls.register_controller(mock_controller)[0]
+                self.bar_test_controller_obj_id = id(cls.controller)
+
+        tr = test_runner.TestRunner(self.tmp_dir,
+                                    test_run_config.test_bed_name)
+        tr.add_test_class(test_run_config, FooTest)
+        tr.add_test_class(test_run_config, BarTest)
+        tr.run()
+        self.assertNotEqual(self.foo_test_controller_obj_id,
+                            self.bar_test_controller_obj_id)
+
+
+if __name__ == "__main__":
+    unittest.main()