Trying to learn about attributes - can someone explain this simple one and why it doesnt work?

TestFunc(1);

[ZeroCheck]
void TestFunc(int value)
{
    Console.WriteLine("Value is not 0");
}

[AttributeUsage(AttributeTargets.Method)]
public class ZeroCheckAttribute : Attribute
{
    public void OnEntry(int value)
    {
        if (value == 0)
        {
            throw new Exception("Cannot proceed as value is 0");
        }
    }
}

TestFunc(1);

[ZeroCheck]
void TestFunc(int value)
{
    Console.WriteLine("Value is not 0");
}

[AttributeUsage(AttributeTargets.Method)]
public class ZeroCheckAttribute : Attribute
{
    public void OnEntry(int value)
    {
        if (value == 0)
        {
            throw new Exception("Cannot proceed as value is 0");
        }
    }
}