added test to use sqrt_power with a negative base as well as corresponding functionality to catch math error

src/main/py/calculations_with_roots.py

@@ -6,4 +6,6 @@ def multiplyRoots(first_number, second_number):
     return sqrt(first_number * second_number)
 
 def sqrt_power(base, exponent):
+    if base < 0:
+        return -1
     return potentiate(sqrt(base), exponent)

src/test/py/test_calculations_with_roots.py

@@ -21,6 +21,9 @@ class calculationsWithRoots(unittest.TestCase):
     def test_sqrt_4_to_power_of_3_should_be_8(self):
         self.assertEqual(sqrt_power(4, 3), 8)
 
+    def test_sqrt_negative_4_to_power_of_3_should_be_negative_one_for_error(self):
+        self.assertEqual(sqrt_power(-4, 3), -1)
+
 
 if __name__ == '__main__':
     unittest.main()