public void Factorial()
{
Assert.AreEqual(1L, GeneralMath.Factorial(0));
var r = new Random();
for (int i = 0; i < 16; i++)
{
int n = -r.Next();
Assert.Throws <ArgumentException>(() => GeneralMath.Factorial(n));
Assert.Throws <ArgumentException>(() => GeneralMath.Factorial((double)n));
}
long currentResult = 1;
for (int multiplier = 1; multiplier <= 20; multiplier++)
{
currentResult *= multiplier;
Assert.AreEqual(currentResult, GeneralMath.Factorial(multiplier));
Assert.AreEqual((double)currentResult, GeneralMath.Factorial((double)multiplier));
}
double currentDoubleResult = currentResult;
for (int multiplier = 21; ; multiplier++)
{
currentDoubleResult *= multiplier;
if (double.IsPositiveInfinity(currentDoubleResult))
{
break;
}
double delta = Math.Pow(10, (long)Math.Log10(currentDoubleResult) - 14);
Assert.AreEqual(currentDoubleResult, GeneralMath.Factorial((double)multiplier), delta, multiplier.ToString());
}
}