test: added mypy to linting tests

requirements-test.txt

 -r requirements.txt
 
 mock==4.0.3
+types-mock==4.0.3
+
 pytest==6.2.2
 pylint==2.7.1
 coverage==5.5
+mypy==0.931

tests/test_lint.py

 from unittest import TestCase
 #pylint: disable=missing-class-docstring,missing-function-docstring
 import pathlib
-from pylint import epylint
-
+from pylint import epylint  # type: ignored
 
 class CodeQualityCase(TestCase):
     def setUp(self):
         self.vcsroot = pathlib.Path(__file__).parent.parent.absolute()
         self.rcfile = self.vcsroot.joinpath('.pylintrc')
 
+        self.module_source_dir = "mattermost_matchmaker"
+        self.test_source_dir = "tests"
+
     def test_source_quality(self):
-        self.assertEqual(0, epylint.lint("mattermost_matchmaker", ["--fail-under=9.5", f"--rcfile={self.rcfile}"]))
+        self.assertEqual(0, epylint.lint(self.module_source_dir, ["--fail-under=9.5", f"--rcfile={self.rcfile}"]))
 
     def test_test_quality(self):
-        self.assertEqual(0, epylint.lint("tests", ["--fail-under=9.5", f"--rcfile={self.rcfile}"]))
+        self.assertEqual(0, epylint.lint(self.test_source_dir, ["--fail-under=9.5", f"--rcfile={self.rcfile}"]))
+
+    def test_source_types(self):
+        #pylint: disable=import-outside-toplevel,no-name-in-module
+        from mypy.build import build as mypy_build
+        from mypy.options import Options as Mypy_Options
+        from mypy.find_sources import create_source_list as mypy_source_list
+
+        options = Mypy_Options()
+        options.config_file=str(self.vcsroot.joinpath("mypy.ini"))
+
+        res = mypy_build(
+            sources=mypy_source_list([str(self.vcsroot.joinpath(self.module_source_dir))], options=options),
+            options=options,
+        )
+
+        self.assertCountEqual(res.errors, [])