public void checkmul()
{
int a = -4;
int b = 4;
int expected = a * b;
int actual = obj.mul(a, b);
Assert.AreEqual(actual, expected, 0, "Result is wrong");
int a2 = int.MaxValue;
int b2 = 23;
Assert.ThrowsException <System.OverflowException>(() => obj.mul(a2, b2));
int a3 = int.MinValue;
int b3 = -2;
Assert.ThrowsException <System.OverflowException>(() => obj.mul(a3, b3));
}