enable branch coverage

Author: rhpvorderman

tox.ini

@@ -9,7 +9,7 @@ passenv=
     PYTHON_ISAL_LINK_DYNAMIC
 commands =
     # Create HTML coverage report for humans and xml coverage report for external services.
-    coverage run --source=isal -m py.test tests
+    coverage run --branch --source=isal -m py.test tests
     # Ignore errors during report generation. Pypy does not generate proper coverage reports.
     coverage html -i
     coverage xml -i