Run coverage over the tests (#504)

diff --git a/.coveragerc b/.coveragerc
index 5bc0e03..e989503 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -1,6 +1,8 @@
 [run]
 branch = True
-source = OpenSSL
+source =
+   OpenSSL
+   tests/
 
 [paths]
 source =