Bonus rounds might look like the more unpredictable part of a slot, especially when reels change, multipliers appear, or completely different features suddenly take over the screen.
Behind all of that, though, the bonus has already been built into the game's maths and tested before players ever get access to it. The best online slots are tested extensively before they reach any real players – not just for quality, but for fairness and reliability, too.
Read on to find out more.
What Tests Are Run on Online Casino Games
In regulated markets, testing can cover the random number generator (RNG), game maths, theoretical RTP, displayed rules and whether the software actually produces the outcomes the original game design says it should.
The UK Gambling Commission's testing requirements, for example, include reviewing RNG source code and documentation, statistically testing RNG output and checking the way those random values are converted into game outcomes. Game testing also covers maths, artwork, rules and theoretical RTP. They then run simulations and manual testing in an environment that reflects the live game.
So if a slot says a particular combination triggers ten free spins, that rule has to work when the finished software is tested. The numbers behind the game need to work as well.
There are a lot of moving parts.
How Developers and iGaming Regulators Test Bonus Rounds
Bonus rounds are part of the game rather than something bolted on after everything else has been tested.
Developers can test whether the correct symbols activate the feature, whether counters and multipliers behave properly, whether the round ends when it should, and whether any winnings are added correctly.
Then there's independent testing where required. The UK Gambling Commission requires approved third-party test houses to assess certain games and software before they're made available to customers.
Its technical standards specifically say that game rules should explain things such as how many or what type of tokens are needed to qualify for a bonus round, as well as the rules and behaviour of that bonus once it begins.
A bonus round might account for part of a slot's theoretical return, so testers need to check the whole game rather than treating the base reels and bonus as unrelated products. Simulations can run huge numbers of game cycles to compare the actual results produced by the software with the theoretical design.
And if a later software change could affect game fairness, such as changing game rules or how RNG results are mapped into outcomes, external retesting may be required.
How Bonus Rounds Are Activated on Online Slots
This part depends entirely on the slot.
A bonus might activate when you land a certain number of scatter symbols. Another game could require you to collect symbols over several spins, fill a meter, or meet some other condition described in the rules.
Sometimes it's immediate. Three qualifying symbols land, and you're straight into the feature. Other bonuses build gradually. Whatever the setup, the game's information or paytable should explain the triggering conditions. Technical standards specifically require rules explaining how players qualify for features and bonus rounds to be available before they gamble.
Once activated, the bonus could introduce free spins, multipliers, different reels, additional wilds or another feature altogether.
But it isn't suddenly operating outside the normal game maths. The trigger conditions, potential payouts and behaviour of the feature have already been programmed and tested as part of the slot.
That's really what all the pre-release testing is for. By the time somebody finally lands the symbols that start a bonus round, the feature should already have been activated, simulated, and checked countless times before.
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