public function testADiffBDifferentFromBDiffAWhenNotEqual(Set $A, Set $B) { $A∖B = $A->difference($B); $B∖A = $B->difference($A); $this->assertNotEquals($A∖B, $B∖A); $this->assertNotEquals($A∖B->asArray(), $B∖A->asArray()); }