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()); }