iter\IterTest::testFlatten PHP Method

    public function testFlatten()
    {
        $this->assertSame([1, 2, 3, 4, 5], toArray(flatten([1, 2, 3, 4, 5])));
        $this->assertSame([1, 2, 3, 4, 5], toArray(flatten([1, [2, 3], 4, [], 5])));
        $this->assertSame([1, 2, 3, 4, 5], toArray(flatten([1, [[2, 3], 4], 5])));
        $this->assertSame([1, 2, 3, 4, 5], toArray(flatten([[1, [[2, [[]], 3], 4]], 5])));
        $this->assertSame([1, 2, 3, 4, 5], toArray(flatten(new \ArrayIterator([new \ArrayIterator([1, 2]), 3, new \ArrayIterator([4, 5])]))));
        // Test key preservation
        $this->assertSame(['a' => 1, 'c' => 2, 'd' => 3], toArrayWithKeys(flatten(['a' => 1, 'b' => ['c' => 2, 'd' => 3]])));
    }