public function testFlatten() { $a = new ArrayWrapper(['item 1' => [1, 2, 3], 'item 2' => [4, 5, 6]]); $arraySingleLevel = $a->flatten(); $this->assertTrue(is_array($arraySingleLevel)); $this->assertCount(6, $arraySingleLevel); $this->assertTrue($arraySingleLevel === [1, 2, 3, 4, 5, 6]); }