public function testAddDoesNothing() { $A = new ImmutableSet([1, 2, 3, 4]); $B = $A->copy(); $A->add(5); $A->add(6); $A->add([7, 8, 9]); $A->add(new Set(['a', 'b'])); $this->assertEquals($B, $A); $this->assertEquals($B->asArray(), $A->asArray()); }