iter\IterTest::testMapKeys PHP Method

    public function testMapKeys()
    {
        $range = range(0, 5);
        $mapped = mapKeys(function ($n) {
            return $n * 3;
        }, $range);
        $this->assertSame([0 => 0, 3 => 1, 6 => 2, 9 => 3, 12 => 4, 15 => 5], toArrayWithKeys($mapped));
        $mapped = mapKeys('strtolower', ['A' => 1, 'B' => 2, 'C' => 3]);
        $this->assertSame(['a' => 1, 'b' => 2, 'c' => 3], toArrayWithKeys($mapped));
    }