MathPHP\SetTheory\SetOperationsTest::testAddTwiceDoesNothing PHP Method

    public function testAddTwiceDoesNothing(array $A, $x, array $R)
    {
        $setA = new Set($A);
        $setR = new Set($R);
        $setA->add($x);
        $setA->add($x);
        $this->assertEquals($setR, $setA);
    }