SomeTest::testFoldLeftRight()

    public function testFoldLeftRight()
    {
        $some = new Some(5);

        $this->assertSame(6, $some->foldLeft(1, function($a, $b) {
            $this->assertEquals(1, $a);
            $this->assertEquals(5, $b);

            return $a + $b;
        }));

        $this->assertSame(6, $some->foldRight(1, function($a, $b) {
            $this->assertEquals(1, $b);
            $this->assertEquals(5, $a);

            return $a + $b;
        }));
    }