Update test_sum_of_digits.py

adding "with" in the test names provides a bit more context about what inputs are being tested against, making the test scenarios clearer and more descriptive for people to read it

solutions/tests/challenge_9/test_sum_of_digits.py

@@ -12,15 +12,15 @@
 class TestSumOfDigits(unittest.TestCase):
     """Tests for the sum_of_digits function."""
 
-    def test_positive_integer(self):
+    def test_with_positive_integer(self):
         """Ensure that the sum of digits of a positive integer is calculated correctly."""
         self.assertEqual(sum_of_digits(123), 6)
 
-    def test_large_integer(self):
+    def test_with_large_integer(self):
         """Ensure that the sum of digits of a large positive integer is calculated correctly."""
         self.assertEqual(sum_of_digits(4567), 22)
 
-    def test_zero(self):
+    def test_with_zero(self):
         """Ensure that the sum of digits of zero is zero."""
         self.assertEqual(sum_of_digits(0), 0)