public function testFeatureProbability()
 {
     $this->assertEquals(0, $this->classifier->featureProbability('the', 'IPC'));
     $this->assertEquals(2 / 3, $this->classifier->featureProbability('out', 'IPC'));
     $this->assertEquals(1 / 3, $this->classifier->featureProbability('component', 'IPC'));
 }