public function testMergeBagsWillReturnANewInstanceWithTheMergedFixtures()
{
$fixture1 = new DummyFixture('foo');
$fixture2 = new MutableFixture('foo', 'Nelmio\\Alice\\Entity\\User', SpecificationBagFactory::create());
$fixture3 = new DummyFixture('bar');
$bag1 = (new FixtureBag())->with($fixture1);
$bag2 = (new FixtureBag())->with($fixture2)->with($fixture3);
$bag3 = $bag1->mergeWith($bag2);
$this->assertInstanceOf(FixtureBag::class, $bag2);
$this->assertSameFixtures(['foo' => $fixture1], $bag1);
$this->assertSameFixtures(['foo' => $fixture2, 'bar' => $fixture3], $bag2);
$this->assertSameFixtures(['foo' => $fixture2, 'bar' => $fixture3], $bag3);
}