public function testCDF($x, $k, $λ, $cdf)
{
$p = Weibull::CDF($x, $k, $λ);
$this->assertEquals($cdf, $p, '', 0.001);
if ($x >= 0) {
$this->assertEquals($x, Weibull::inverse($p, $k, $λ), '', 0.001);
}
}