<?

public function testNoNewStarsAppeared(): void
  {
     $expectedStars = $this->historicStarsOnFrame();
     $observedStars = $this->starsFromObservation();
     //These sentences get a very large collection

     $this->assertEquals($expectedStars, $observedStars);
     //If something fails we will have a very hard debugging time
    }

<?

public function testNoNewStarsAppeared(): void
  {
     $expectedStars = $this->historicStarsOnFrame();
     $observedStars = $this->starsFromObservation();
     //These sentences get a very large collection

     $newStars = array_diff($expectedStars, $observedStars);

     $this->assertEquals($expectedStars, $observedStars ,
         'There are new stars ' . print_r($newStars,true));
     //Now we can see EXACTLY why the assertion failed with a clear and
     //Declarative Message 
    }