Illuminate\Support\Collection::union PHP Method

    public function union($items)
    {
        return new static($this->items + $this->getArrayableItems($items));
    }

 public function testUnionCollection()
 {
     $c = new Collection(['name' => 'Hello']);
     $this->assertEquals(['name' => 'Hello', 'id' => 1], $c->union(new Collection(['name' => 'World', 'id' => 1]))->all());
 }