WIP

tox.ini

diff --git a/tox.ini b/tox.ini
index d40fb01..7282f97 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,11 +1,17 @@
 [tox]
-envlist = py27,pypy,py35,py36,py37,py38
+envlist = py27,pypy,py35,py36,py37,py38,coverage
 
 [testenv]
 deps =
     Cython
-    codecov
 commands =
     python setup.py test
+
+[testenv:coverage]
+deps =
+    Cython
+    codecov
+commands =
+    pytest --cov --cov-append
     codecov
 passenv = CI TRAVIS TRAVIS_*