Functional\Tests\GroupTest::test PHP Method

    public function test()
    {
        $fn = function ($v, $k, $collection) {
            InvalidArgumentException::assertCollection($collection, __FUNCTION__, 3);
            return is_int($k) ? $k % 2 == 0 : $v[3] % 2 == 0 ? 'foo' : '';
        };
        $this->assertSame(['foo' => [0 => 'value1', 2 => 'value3'], '' => [1 => 'value2', 3 => 'value4']], group($this->list, $fn));
        $this->assertSame(['foo' => [0 => 'value1', 2 => 'value3'], '' => [1 => 'value2', 3 => 'value4']], group($this->listIterator, $fn));
        $this->assertSame(['' => ['k1' => 'val1', 'k3' => 'val3'], 'foo' => ['k2' => 'val2']], group($this->hash, $fn));
        $this->assertSame(['' => ['k1' => 'val1', 'k3' => 'val3'], 'foo' => ['k2' => 'val2']], group($this->hashIterator, $fn));
    }