public function testConvertToArray()
 {
     $collection = new BasicCollection();
     $collection->add('foo');
     $collection->add('bar');
     $collection->add('baz');
     $collection->remove('bar');
     // this call should not create a gap in the index sequence
     $actual = $collection->toArray();
     $expected = [0 => 'foo', 1 => 'baz'];
     self::assertEquals($expected, $actual);
 }