public function testSimpleDistances()
{
$Distance = new Distance();
$this->assertTrue($Distance->isZero());
$this->assertFalse($Distance->isNegative());
$this->assertEquals(10, $Distance->set(10)->kilometer());
$this->assertEquals(20, $Distance->multiply(2)->kilometer());
$this->assertEquals(21.1, $Distance->add(new Distance(1.1))->kilometer());
$this->assertFalse($Distance->isZero());
$this->assertEquals(-0.9, $Distance->subtract(new Distance(22))->kilometer());
$this->assertTrue($Distance->isNegative());
}