Last weekend, I watched the movie Passengers. The basic plot of the movie is that two passengers in hibernation on a flight from Earth to another planet are awakened ninety years too early. As a QA engineer the movie got me thinking about two valuable lessons for developing and testing software.
Lesson One: “And Yet It Did”
In Passengers, when Jim’s hibernation pod fails, he tells the ship’s computer, the android bartender, and even another human what has happened. The response of all three is “Well, that’s impossible. The hibernation pods never fail.” Jim’s response is “Then how do you explain the fact that I’m here?” Many times in my testing career I have been told by developers that the behavior I am observing in our software is impossible. And I always respond with “And yet, here is the behavior that I’m seeing”. In one particular instance at a previous company, I was testing that information entered into the third-party software we integrated with was making it into our software. This testing was going well, until one entry didn’t travel to our software. I told the developer about it. He said, “That’s impossible. I’ve tested this, and you’ve been testing this for days.” I said, “Yes, and yet, this record wasn’t saved.” He said, “Look at the logs- you can see that the information was sent.” I said, “Yes, and yet, it wasn’t saved.” He said, “I entered more information just now, and you can see that it was saved.” I said, “Yes, and yet, the information I entered was not saved.” After much investigation, it was finally discovered that there was a bug where the database was not saving any record after the 199th record. Because I was testing in a different table than he was, and he didn’t have as many records, he didn’t see the error. The moral of the story: Even if something is impossible, it might still happen.
Lesson Two: “But What If It Did?”
One of the scariest parts of Passengers for me was that there was no way for Jim to reboot his hibernation pod and return to hibernation. Also, there were no spare pods. Even worse, there was no way for him to wake up the captain or any human who could help him. I found myself yelling at the screen, “How is this even possible? Why didn’t they put in contingency plans?” The answer, of course, is that the designers of the system were SO SURE that nothing could ever go wrong with the pods. But something did go wrong, and due to their false confidence there was no way to make it right. QA engineers are always thinking about all the possible ways that software can fail. I have often heard the argument “But no sane user would do that.” And I always respond with “But what if they did?” While we may not have time to account for every possible way that our software might fail, we should create appropriate responses for as many ways as we can, and log the rest for future fixes.
I like to think that somewhere on Earth in the Passengers universe, a QA engineer is saying to her product owners at the spaceship design company, “See, I TOLD you the pods could fail!”