Add basic unit tests

README.md

@@ -1 +1,9 @@
 # test123
+
+Simple demo project with a basic unit test.
+
+## Run tests
+
+```bash
+python3 -m unittest test_test_example.py
+```

test_example.py

@@ -0,0 +1,3 @@
+def add(a: int, b: int) -> int:
+    """Return the sum of two integers."""
+    return a + b

test_test_example.py

@@ -0,0 +1,18 @@
+import unittest
+
+from test_example import add
+
+
+class TestAdd(unittest.TestCase):
+    def test_add_positive_numbers(self):
+        self.assertEqual(add(2, 3), 5)
+
+    def test_add_negative_numbers(self):
+        self.assertEqual(add(-1, -1), -2)
+
+    def test_add_zero(self):
+        self.assertEqual(add(0, 42), 42)
+
+
+if __name__ == "__main__":
+    unittest.main()