Run tests in parallel via tox

tox.ini

@@ -9,11 +9,16 @@ env_list =
 [testenv]
 deps =
     numpy
+    pytest-sugar
 extras =
     tests
 commands =
     {envpython} selftest.py
-    {envpython} -m pytest -W always {posargs}
+    {envpython} -m pytest \
+      --dist worksteal \
+      --numprocesses auto \
+      -W always \
+      {posargs}
 
 [testenv:lint]
 skip_install = true