Add mypy to test requirements

Author: vitalk

pyproject.toml

@@ -4,3 +4,12 @@ requires = [
   "setuptools-scm[toml]",
 ]
 build-backend = "setuptools.build_meta"
+
+[tool.mypy]
+warn_unreachable = true
+warn_unused_ignores = true
+warn_redundant_casts = true
+enable_error_code = [
+    "ignore-without-code",
+    "truthy-bool",
+]

requirements/test.txt

@@ -2,3 +2,4 @@ mock
 pylint
 coverage
 pytest-pep8
+mypy