public function testOffsetExists()
 {
     $this->assertTrue($this->object->offsetExists('1A'));
     $this->assertTrue($this->object->offsetExists('2A'));
     $this->assertTrue($this->object->offsetExists('3A'));
     $this->assertFalse($this->object->offsetExists('XX'));
     $this->assertFalse($this->object->offsetExists(-1));
     $this->assertFalse($this->object->offsetExists(''));
 }
 public function testOffsetUnset()
 {
     $this->object->offsetUnset('1A');
     $this->assertEquals(2, $this->object->count());
     $this->assertFalse($this->object->offsetExists('1A'));
 }