diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ef176e0
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+coverage.xml
+.coverage
diff --git a/setup.cfg b/setup.cfg
index ff07ac7..a193373 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -9,5 +9,16 @@ skip = .venv,.tox
 extend-ignore = E203,E501
 extend-exclude = .venv
 
+[tool:pytest]
+addopts =
+    --cov-report term-missing --cov-branch --cov-report xml --cov-report term
+    --cov=tests.code -vv --strict-markers -rfE
+
+filterwarnings =
+    error
+
 [mypy]
 no_implicit_optional = True
+
+[mypy-django.*,importlib_metadata.*,psycopg2.*,aiopg.*]
+ignore_missing_imports = True
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/code.py b/tests/code.py
new file mode 100644
index 0000000..972a635
--- /dev/null
+++ b/tests/code.py
@@ -0,0 +1,10 @@
+from typing import Optional
+
+
+def code(arg: Optional[bool]) -> str:
+    if arg is None:
+        return "a"
+    elif arg is True:
+        return "b"
+    else:
+        return "c"
diff --git a/tests/requirements.txt b/tests/requirements.txt
new file mode 100644
index 0000000..9955dec
--- /dev/null
+++ b/tests/requirements.txt
@@ -0,0 +1,2 @@
+pytest
+pytest-cov
diff --git a/tests/test_code.py b/tests/test_code.py
new file mode 100644
index 0000000..d3e4c7d
--- /dev/null
+++ b/tests/test_code.py
@@ -0,0 +1,8 @@
+import pytest
+
+from . import code
+
+
+@pytest.mark.parametrize("arg, expected", [(None, "a")])
+def test_code(arg, expected):
+    assert code.code(arg) == expected