Export the absolute key path for the authentication of GTS tests.

Exporting relative key path isn't robust for GTS tests because developer
might run tests without under the root directory and this will fail the
tests. This issue can be resolved by exporting the absolute key path.

Bug: 153379982
Test: atest atest_unittests
Change-Id: Ia2b2ace83656c5c34a607c4a7df572b7ddc72056
diff --git a/atest/test_runners/atest_tf_test_runner.py b/atest/test_runners/atest_tf_test_runner.py
index 5380423..6f26c6d 100644
--- a/atest/test_runners/atest_tf_test_runner.py
+++ b/atest/test_runners/atest_tf_test_runner.py
@@ -107,7 +107,7 @@
         key_path = os.path.join(self.root_dir, ape_api_key)
         if ape_api_key and os.path.exists(key_path):
             logging.debug('Set APE_API_KEY: %s', ape_api_key)
-            os.environ['APE_API_KEY'] = ape_api_key
+            os.environ['APE_API_KEY'] = key_path
         else:
             logging.debug('APE_API_KEY not set, some GTS tests may fail'
                           ' without authentication.')
diff --git a/atest/test_runners/atest_tf_test_runner_unittest.py b/atest/test_runners/atest_tf_test_runner_unittest.py
index d1968e8..5344ba0 100755
--- a/atest/test_runners/atest_tf_test_runner_unittest.py
+++ b/atest/test_runners/atest_tf_test_runner_unittest.py
@@ -306,13 +306,13 @@
         self.tr._try_set_gts_authentication_key()
         mock_exist.assert_not_called()
 
-    @mock.patch('constants.GTS_GOOGLE_SERVICE_ACCOUNT')
-    @mock.patch('os.path.exists')
-    def test_try_set_gts_authentication_key_not_set(self, mock_exist, mock_key):
+    @mock.patch('os.path.join', return_value='/tmp/file_not_exist.json')
+    def test_try_set_gts_authentication_key_not_set(self, _):
         """Test try_set_authentication_key_not_set method."""
-        # Test key neither exists nor set by user.
-        mock_exist.return_value = False
-        mock_key.return_value = ''
+        # Delete the environment variable if it's set. This is fine for this
+        # method because it's for validating the APE_API_KEY isn't set.
+        if os.environ.get('APE_API_KEY'):
+            del os.environ['APE_API_KEY']
         self.tr._try_set_gts_authentication_key()
         self.assertEqual(os.environ.get('APE_API_KEY'), None)