MCordingley\Regression\Observations::add PHP Method

    public function add(array $features, float $outcome) : self
    {
        return $this->addObservation(new Observation($features, $outcome));
    }

 public function testBadObservationsCount()
 {
     $observations = new Observations();
     $observations->add([1, 2, 3], 4);
     static::setExpectedException('InvalidArgumentException');
     $observations->add([1, 2], 4);
 }