public function testThatCollectionItemsCanBeGroupedByItemProperty()
{
$items = [["a" => "b"], ["a" => "b", "b" => "c"], ["c" => "d"], ["a" => "c"]];
//group by single property
$grouped = CollectionUtility::groupByProperty($items, "a");
$this->assertEquals(["b" => [["a" => "b"], ["a" => "b", "b" => "c"]], "c" => [["a" => "c"]], "" => [["c" => "d"]]], $grouped);
//... or properties
$items[] = ["a" => "b", "b" => "c", "c" => "d"];
$grouped = CollectionUtility::groupByProperty($items, ["b", "a"]);
$this->assertEquals([".b" => [["a" => "b"]], "c.b" => [["a" => "b", "b" => "c"], ["a" => "b", "b" => "c", "c" => "d"]], ".c" => [["a" => "c"]], "." => [["c" => "d"]]], $grouped);
}
