doc: tests should fail without the change

Author: arnehormann

PULL_REQUEST_TEMPLATE.md

@@ -3,7 +3,7 @@ Please explain the changes you made here.
 
 ### Checklist
 - [ ] Code compiles correctly
-- [ ] Created tests, if possible
+- [ ] Created tests which fail without the change (if possible)
 - [ ] All tests passing
 - [ ] Extended the README / documentation, if necessary
 - [ ] Added myself / the copyright holder to the AUTHORS file