public function test_map_assoc_returns_array() { $input = ['x' => 1, 'y' => 2, 'z' => 3]; $expected = [['x', 1], ['y', 2], ['z', 3]]; $actual = map($input, function ($v, $k) { return [$k, $v]; }); $this->assertSame($expected, $actual); }