topogen: don't backtrace when topogen is not used

This allows old tests to be run with '--topology-only' without
generating tons of error messages, instead it will just stop the test
without trying anything else.

diff --git a/tests/topotests/conftest.py b/tests/topotests/conftest.py
old mode 100644 (file)
new mode 100755 (executable)
index e042a3d..a8bc539
--- a/tests/topotests/conftest.py
+++ b/tests/topotests/conftest.py
@@ -21,6 +21,9 @@ def pytest_runtest_call():
     # pylint: disable=E1101
     # Trust me, 'config' exists.
     if pytest.config.getoption('--topology-only'):
-        # Allow user to play with the setup.
-        get_topogen().mininet_cli()
+        tgen = get_topogen()
+        if tgen is not None:
+            # Allow user to play with the setup.
+            tgen.mininet_cli()
+
         pytest.exit('the topology executed successfully')