public function testIncorrectInput()
{
// The input $source is neither a callback or a set of arrays
$this->setExpectedException('MathPHP\\Exception\\BadDataException');
$x = 10;
$incorrectFunction = $x ** 2 + 2 * $x + 1;
NumericalDifferentiation::getPoints($incorrectFunction, [0, 4, 5]);
}