Add tests folder and first util test

tests/test_util.py

@@ -0,0 +1,10 @@
+"""Tests for the `util` module."""
+import pytest
+import util.convert as uc
+
+
+def test_convert_string_to_integer() -> None:
+    assert uc.convert_string_to_integer("0") == 0
+    assert uc.convert_string_to_integer("3.14") == 3
+    with pytest.raises(uc.InvalidStringException) as exc:
+        uc.convert_string_to_integer("a")