sum_of_multiples: add tests for logic and input validation

sum-of-multiples/example.py

@@ -1,13 +1,13 @@
 class SumOfMultiples(object):
 
     def __init__(self, *args):
-        self.numbers = args if args else [3, 5]
+        self.numbers = args or (3, 5)
 
     def to(self, limit):
         return sum(n
                    for n in range(limit)
                    if self.is_multiple(n))
 
     def is_multiple(self, m):
-        return any(m % n == 0
+        return any(n != 0 and m % n == 0
                    for n in self.numbers)

sum-of-multiples/sum_of_multiples_test.py

@@ -7,7 +7,7 @@ class SumOfMultiplesTest(unittest.TestCase):
     def test_sum_to_1(self):
         self.assertEqual(0, SumOfMultiples().to(1))
 
-    def test_sum_to_3(self):
+    def test_sum_to_4(self):
         self.assertEqual(3, SumOfMultiples().to(4))
 
     def test_sum_to_10(self):
@@ -22,6 +22,15 @@ def test_configurable_7_13_17_to_20(self):
     def test_configurable_43_47_to_10000(self):
         self.assertEqual(2203160, SumOfMultiples(43, 47).to(10000))
 
+    def test_configurable_20_24_25_to_800(self):
+        self.assertEqual(36144, SumOfMultiples(20, 24, 25).to(800))
+
+    def test_configurable_0_to_10(self):
+        self.assertEqual(0, SumOfMultiples(0).to(10))
+
+    def test_configurable_0_1_to_10(self):
+        self.assertEqual(45, SumOfMultiples(0, 1).to(10))
+
 
 if __name__ == '__main__':
     unittest.main()