Seems to need zope.testrunner, too.

.travis.yml

@@ -9,7 +9,7 @@ python:
   - pypy-5.4.1
   - pypy3
 install:
-  - pip install -U pip setuptools
+  - pip install -U pip setuptools zope.testrunner
   - pip install -U coveralls coverage
   - pip install -U -e ".[test]"
 script: