Add sub two challenge

math_probability/sub_two/test_sub_two.py

@@ -0,0 +1,22 @@
+from nose.tools import assert_equal, assert_raises
+
+
+class TestSubTwo(object):
+
+    def test_sub_two(self):
+        solution = Solution()
+        assert_raises(TypeError, solution.sub_two, None)
+        assert_equal(solution.sub_two(7, 5), 2)
+        assert_equal(solution.sub_two(-5, -7), 2)
+        assert_equal(solution.sub_two(-5, 7), -12)
+        assert_equal(solution.sub_two(5, -7), 12)
+        print('Success: test_sub_two')
+
+
+def main():
+    test = TestSubTwo()
+    test.test_sub_two()
+
+
+if __name__ == '__main__':
+    main()