So you are about to plan for how to test the game you are developing, or preferably – will start to develop. Where do you start? Maybe you have some understanding of what it is that you are going to develop. Requirements, or stakeholders that are telling you what should be in the game, and how it should work to some degree. But often this only covers a small portion of the complete test space. I use “test space” to denote the complete set of tests you would have to run to test absolutely everything.
You know that you will never cover the entire test space with tests, since this would not be very cost effective. But you probably have some idea that just testing the core functionality of the game works will not be enough. It will always be a priority question just which tests you will actually perform, but how do you think of all the tests that you would possibly need in the first place?
In this article I will try to give a list of different types of test that I think should at least be considered before development of a new game starts. I will use ISO 25010  as a base, and add thoughts from James Bach  and James Whittaker  who have developed different approaches for exploratory testing, which will help to think about other ways to explore the test space. This will not be a complete, all-comprehensive list, but my hope is that it will be a good start.
ISO 25010 is a quality model for systems and software. It contains eight categories of software quality, which can be good to use as a starting point when designing tests.
This category covers a large test space, and it is easy to completely miss large parts of it if you do not take them time to think through your approach.
The degree to which the product provides functions that meet stated and implied needs when the product is used under specified conditions . A user action should lead to some kind of result. When I press the “New Game” button something should happen. When a press the mouse button in game it has some effect depending on where the cursor is located. When a user presses “Connect to Social Media Platform” the game should connect to said social medial platform. And so on. A large chunk of your tests will probably end up in this category, and these are most likely the first ones you think of.
Also included in this category, and equally obvious, would be artificial intelligence. Is the AI taking appropriate actions based on specified conditions? Same goes for audio – are the correct audio files played based on specified conditions? Verifying game mechanics are included here as well. Same thing with physics engines.
Another big thing, depending on the game under test, would be verifying that the game world meets stated or implied needs. Is everything in the right place? A rock, a vendor, monsters, NPCs, caves, castles, houses, lakes, mountains etc.
Multiplayer functionality is also part of functional suitability.
There are obviously many different types of tests in this category, and they vary wildly between different genres and games. Trying to create a complete overview map of all functional suitability tests for different genres is a whole article in itself. And even then a specific game could deviate from the genre and require other unique tests.
How to come up with tests for all these different areas is not an easy task. In a previous article I mentioned using Systematic Inventive Thinking as one way think creatively around what to test, by starting with a normal user behavior and applying SIT. 
So apart from the functional suitability tests, another category of tests is reliability tests. The degree to which a system or component performs specified functions under specified conditions for a specified period of time.
Fault tolerance is one aspect. What happens when something goes wrong? Will the game crash, or will the game handle the fault in a suitable way?
Recovery is another. What happens when the game actually crashes? What happens with user data? Progression, items, scores, etc. Preferably the game should never crash, but if it does, it should have minimal impact on the user.
Duration and maturity tests is also included in the reliability category. What happens if you leave the game on for 24 hours? A week? Memory leaks could typically be found by this kind of tests. How does the game run after 12 hours of intensive playing? Any performance degrades? Any other degrades?
In this category I would also include random automated tests that click through the UI, and tests that drop automated bots into a game world and let them traverse the world randomly until they pass the walls of the game world – this could for example let you find places where characters models could get stuck in the world.
Stress testing is also part of reliability testing. In it’s simplest form it can include tests like pressing a button many times instead of one. It can also include thousands of users logging into a server at the same time, or hundreds of players fighting in PvP against each other, or participating in a public non-instanced quest together. Another example is a large amount of players performing microtransactions simultaneously. Under the reliability umbrella we are looking for if the game can handle these situations, and will not crash, log you out or something similar, not the performance under these conditions, which is covered by the Performance Efficiency category below.
The degree to which the product has attributes that enable it to be understood, learned, used and attractive to the user, when used under specified conditions . So what does this actually mean?
Easy of use, learability, attractiveness. Is the game easy to start playing? Can the user understand the game mechanics? Is the user interface understandable? Is the tutorial good?
But this could also include fun factor testing when it comes to game. Is the game actually fun to play? Realism testing could also be included in this category, which includes the believability of the physics engine and many other things. Is the game realistic and immersive to the player? Balancing could also be included here as it can correlate to if the game is fun and understandable.
The performance relative to the amount of resources used under stated conditions . This can include response time, loading time, and different kinds of time behavior. It can also include different types of resource utilization, such as RAM, GPU AND CPU usage. FPS would be connected to that resource utilization.
This also includes performance tests under stressful conditions, such as relative FPS when fighting alongside 10 people in PvP versus 200 people.
Many of these tests also impact how attractive the game is to the user, which we talked about in the operability section.
The degree of protection of information and data so that unauthorized persons or systems cannot read or modify them and authorized persons or systems are not denied access to them . In a single player game without any microtransactions, security is important. But this importance explodes when testing an MMO, MOBA or similar game. Confidentiality, integrity, accountability, authenticity . Security testing requires very specific competence compared to other types of testing, but is essential to modern games. How to battle botting and gold sellers can be included in this category.
The degree to which two or more systems or components can exchange information and/or perform their required functions while sharing the same hardware or software environment .
Interoperability is part of this. Support for different game pads, gaming mouses, keyboards, Oculus and Morpheus, and similar gaming paraphernalia. One software system – the game – and one or more hardware systems.
Co-existence between programs. Having Spotify running in the background. Running Team Speak, Ventrilo or other VoIP clients. Two or more different software system co-existing.
The degree of effectiveness and efficiency with which the product can be modified . Many activities included in this category are development activities. But securing testability  is definitely something of interest to the game tester.
You could include testing for modification  support in this category.
The degree to which a system or component can be effectively and efficiently transferred from one hardware, software or other operational or usage environment to another .
Here we can test on different hardware and OS. Mobile games need to be tested on iOS, Android and Kindle for example. Then there are different manufacturers of hardware. Different OS versions. Different versions of the hardware from the same manufacturer. For PC there is an unlimited number of configurations. Here the key would be to have enough business information to be able to prioritize different hardware and OS configurations, framed by minimum and recommended hardware requirements.
Heuristics by James Bach 
James Bach, one of the most famous software testing experts, has created a list of general test techniques that are simple and universal enough to be applicable in many different contexts, and can also be applied to game testing. This is another way of looking at the test space compared to the categories that I have previously presented. Attacking the problem from a different angle.
To better understand this, look into the reference and read the document.
Testing Tours by James Whittaker 
James Whittaker is a professor and software testing evangelist at Microsoft, and has previously worked at Google as well. During his time on Google he developed a way of performing exploratory testing  which he called Testing Tours. Testing Tours can also be applied to explore the testing space, but takes yet another different approach in doing so than the two previous approaches.
“Suppose you are visiting a large city like London, England, for the very first time. It’s a big, busy, confusing place for new tourists, with lots of things to see and do. Indeed, even the richest, most time-unconstrained tourist would have a hard time seeing everything a city like London has to offer. The same can be said of well-equipped testers trying to explore complex software; all the funding in the world won’t guarantee completeness.” 
So James Whittaker created a number of “Testing Tours” that you could perform to explore the software under test, based on this tourism metaphor.
To better understand this, look into the reference and read the document.
This has been my attempt to give a good base for continued exploration of the test space to help new testers or developers think of all the necessary tests they need to run for their game.
This is by no means the only way to tackle this problem, but I usually combine these three approaches when I think about a testing problem.
Unfortunately this is just the first step. The next step is to prioritize the different tests, since running them all is not feasible. But that is a topic for another article.
 ISO/IEC 25010:2011
 James Bach
 James Whittaker
 Systematic Inventive Thinking and Game Testing
 Video Game Mod
 Heuristic Test Strategy Model
 Testing Tours
 Exploratory Testing