public function testContainsKey() { $elements = [1, 'A' => 'a', 2, 'null' => null, 3, 'A2' => 'a', 'B2' => 'b']; $collection = new ArrayCollection($elements); $this->assertTrue($collection->containsKey(0), 'Contains index 0'); $this->assertTrue($collection->containsKey('A'), 'Contains key "A"'); $this->assertTrue($collection->containsKey('null'), 'Contains key "null", with value null'); $this->assertFalse($collection->containsKey('non-existent'), "Doesn't contain key"); }