1 files changed, 6 insertions, 1 deletions
diff --git a/tox.ini b/tox.ini
index 8ac2e18..291442d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,8 +2,13 @@
 envlist = py27, py35, py36, py37, pypy
 
 [testenv]
+# For performance, but also for using "source" with coveragepy (https://github.com/nedbat/coveragepy/issues/268).
+usedevelop = True
 deps =
     pytest
-    pytest-cov
+    coverage: coverage
+    coverage: pytest-cov
+setenv =
+    coverage: PYTEST_ADDOPTS=--cov --cov-report=term-missing
 commands =
     py.test {posargs}