use the right version of coverage
Index: runtests.sh
--- runtests.sh.orig
+++ runtests.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
-if which coverage > /dev/null; then
-    coverage run tests/tests.py
-    coverage report
+if which coverage${MODPY_MAJOR_VERSION} > /dev/null; then
+    coverage${MODPY_MAJOR_VERSION} run tests/tests.py
+    coverage${MODPY_MAJOR_VERSION} report
 else
     /usr/bin/env python tests/tests.py
 fi