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 * $x + 1;
     Interpolation::getPoints($incorrectFunction, [0, 4, 5]);
 }