public void checksub()
{
int a = -4;
int b = 4;
int expected = a - b;
int actual = obj.sub(a, b);
Assert.AreEqual(actual, expected, 0, "Result is wrong");
int a1 = int.MaxValue;
int b1 = int.MinValue;
Assert.ThrowsException <System.OverflowException>(() => obj.sub(a1, b1));
int a2 = int.MaxValue;
int b2 = -23;
Assert.ThrowsException <System.OverflowException>(() => obj.sub(a2, b2));
int a3 = int.MinValue;
int b3 = 2;
Assert.ThrowsException <System.OverflowException>(() => obj.sub(a3, b3));
}