Add pytest and mypy steps to the pre-commit hooks to avoid committing clearly broken code

.pre-commit-config.yaml

@@ -15,3 +15,17 @@ repos:
         args:
           - --fix=lf
       - id: trailing-whitespace
+  - repo: local
+    hooks:
+      - id: pytest
+        name: Check pytest unit tests pass
+        entry: pipenv run pytest
+        pass_filenames: false
+        language: system
+        types: [python]
+      - id: mypy
+        name: Check mypy static types match
+        entry: pipenv run mypy . --ignore-missing-imports
+        pass_filenames: false
+        language: system
+        types: [python]