diff --git a/calc_mul.py b/calc_mul.py
index b55a367..df6c7cc 100755
--- a/calc_mul.py
+++ b/calc_mul.py
@@ -1,34 +1,23 @@
-#!/usr/bin/python3
+#! /usr/bin/python3
+
+def calc(A, B):
+    if not isinstance(A, int) or not isinstance(B, int):
+        return -1
+    ai = int(A)
+    bi = int(B)
+    if 1 <= ai <= 999 and 1 <= bi <= 999:
+        return ai * bi
+    else:
+        return -1
+
+def main():
+    match_string = ''
+    while match_string != 'end':
+        A = input('input A: ')
+        B = input('input B: ')
+        print('input A * input B =', calc(A, B))
 
-import re
-                
-def calc(A,B):
-        ai=str(A)
-        bi=str(B)
-        p = re.compile('\d+(\.\d+)?')
-        if p.match(ai) or p.match(bi):
-                a=float(ai)
-                b=float(bi)
-                if 0<a and a<b and b<1000:
-                        valid=True
-                else:
-                        valid=False
-        else:
-                valid=False
-                
-        if valid:
-                ans=a*b
-                return ans
-        else:
-                return -1
-        
-                
-def main ():
-	matchstring = ''
-	while matchstring != 'end':
-                A = input ('input A: ')
-                B = input ('input B: ')
-                print ('input A * input B = ', calc(A,B))
 
 if __name__ == '__main__':
-	main()
+    main()
+
diff --git a/test_cases.py b/test_cases.py
index 6f08065..87f1391 100644
--- a/test_cases.py
+++ b/test_cases.py
@@ -1,21 +1,38 @@
-#!/usr/bin/python3
-
 import unittest
 from calc_mul import calc
 
-# Run with testrunner so needs to be in file test_
-
-class TestCalc (unittest.TestCase):
-
-        def test_sample1 (self):
-                self.assertEqual (21, calc(3,7))
-
-        def test_sample2 (self):
-                self.assertEqual (-1, calc(0,150))
-
-        def test_sample3 (self):
-                self.assertEqual (-1, calc('a','b'))
-
-        def test_sample4 (self):
-                self.assertEqual (-1, calc(0.1,999))
+class TestCalc(unittest.TestCase):
+
+    # Normal valid inputs
+    def test_valid_cases(self):
+        self.assertEqual(1, calc(1, 1))  # Minimum boundary
+        self.assertEqual(200, calc(10, 20))  # Valid value
+        self.assertEqual(998001, calc(999, 999))  # Maximum boundary
+
+    # Invalid integer inputs (out of range)
+    def test_out_of_range(self):
+        self.assertEqual(-1, calc(0, 100))  # Just before minimum boundary
+        self.assertEqual(-1, calc(1000, 5))  # Just after maximum boundary
+        self.assertEqual(-1, calc(-5, 500))  # Negative number
+        self.assertEqual(-1, calc(500, 1001))  # One value out of range
+
+    # Invalid non-integer inputs
+    def test_invalid_types(self):
+        self.assertEqual(-1, calc(1.5, 2))  # Float
+        self.assertEqual(-1, calc("10", 5))  # String number
+        self.assertEqual(-1, calc(5, 'y'))  # String character
+        self.assertEqual(-1, calc('a', 'b'))  # Both are strings
+        self.assertEqual(-1, calc(None, 5))  # None as input
+        self.assertEqual(-1, calc(10, None))  # None as second input
+        self.assertEqual(-1, calc([], 5))  # List as input
+        self.assertEqual(-1, calc({}, 10))  # Dictionary as input
+
+    # Completely invalid inputs
+    def test_both_invalid(self):
+        self.assertEqual(-1, calc(-1, 'x'))  # One negative, one string
+        self.assertEqual(-1, calc('x', None))  # String and None
+        self.assertEqual(-1, calc(1000, 0.5))  # Out of range and float
+
+if __name__ == "__main__":
+    unittest.main()