Merge pull request #233 from blueyed/improve-pdb-usage-error

Improve UsageError when used with --pdb

xdist/plugin.py

@@ -115,7 +115,7 @@ def pytest_cmdline_main(config):
         if val("dist") != "no":
             if usepdb:
                 raise pytest.UsageError(
-                    "--pdb incompatible with distributing tests.")
+                    "--pdb is incompatible with distributing tests; try using -n0.")  # noqa: E501
 
 # -------------------------------------------------------------------------
 # fixtures