Add mypy to tox env

Author: vitalk

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{37,38,39,linting}
+    py{37,38,39,linting},mypy
 
 [pytest]
 norecursedirs = .git .tox env coverage docs
@@ -16,6 +16,7 @@ deps=
     -rrequirements/test.txt
     -rrequirements/docs.txt
     pre-commit>=1.11.0
+    mypy>=1.6.1
     tox
 basepython = python3.8
 usedevelop = True
@@ -56,6 +57,11 @@ basepython = python3.8
 deps = pre-commit>=1.11.0
 commands = pre-commit run --all-files --show-diff-on-failure {posargs:}
 
+[testenv:mypy]
+basepython = python3.8
+deps = mypy>=1.6.1
+commands = mypy src
+
 [testenv:docs]
 changedir = docs
 skipsdist = True