Quickly running PHP code online is a best way to test something. It gives instantly a setup that help us run our PHP code. This online setup can work from anywhere we have Internet access and not just from development machine.
I today tested two of the online App and both worked correctly. One is compileonline.com and another is writecodeonline.com
There are few caveat though. Many functions related to fine may not run due to security reasons. I have tried realpath() and compileonline has given me message regarding security. Another one has not given any message which is bad.