{
        name      => 'two keys',
        group_by  => ['key1', 'key2'],
        group_how => {
            count => 'count',
        },
        input => [
            {
                key1  => 'a',
                key2  => 'a',
            },
            {
                key1  => 'a',
                key2  => 'a',
            },
            {
                key1  => 'a',
                key2  => 'a',
            },
            {
                key1  => 'a',
                key2  => 'b',
            },
            {
                key1  => 'a',
                key2  => 'b',
            },
        ],
        expected => [
            {
                key1  => 'a',
                key2  => 'a',
                count => 3,
            },
            {
                key1  => 'a',
                key2  => 'b',
                count => 2,
            },
        ],
    },