Add a mypy env to tox

This will enable typechecking during testing.

1 files changed, 9 insertions, 1 deletions

diff --git a/tox.ini b/tox.ini
index 2e3d0df..f89ee8f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,7 @@
 
 [tox]
 envlist =
-    flake8, py35, py36, py37, py38, py39
+    flake8, mypy, py35, py36, py37, py38, py39
 # Other valid evironments are:
 #   docs
 #   release
@@ -52,6 +52,14 @@ commands =
     twine check dist/*
 skip_install = true
 
+# Type checking
+[testenv:mypy]
+deps =
+    mypy
+commands =
+    mypy natsort
+skip_install = true
+
 # Build documentation.
 # sphinx and sphinx_rtd_theme not in docs/requirements.txt because they
 # will already be installed on readthedocs.