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Connectivity Assist and speed tests
When Wi-Fi gets weak, your phone can quietly move some connections to mobile data so the internet doesn't cut out. That's useful day to day, but in a speed test it makes your Wi-Fi look faster than it is and uses up your mobile data. This page explains what's going on and how to turn it off.
What does this feature do?
On iPhone and iPad it's called Connectivity Assist (Wi-Fi Assist on older versions of iOS). On Android phones it usually sits in the Wi-Fi settings as Switch to mobile data or something similar.
Both do the same thing: when Wi-Fi slows down or stalls, the phone opens some connections over mobile data without asking you, so pages and apps keep loading.
Why does it throw off a speed test?
A speed test opens several connections at once so it can use your internet at full capacity. If some of them move to mobile data, the number you get is Wi-Fi and mobile data added together. The screen still says "Wi-Fi", but the result no longer shows the speed of your Wi-Fi on its own.
The test also eats into your mobile data allowance while it runs. In one of our own measurements, about 35 of the 133 Mbps shown as Wi-Fi was coming from mobile data, and a single test used 68 MB of mobile data.
What happens in the HIZTESTI app?
When a test starts on Wi-Fi, the HIZTESTI app for iPhone and iPad runs it over Wi-Fi only: every measurement connection is tied to Wi-Fi and never moves to mobile data. So a Wi-Fi test in the app doesn't use your mobile data, and the result shows your Wi-Fi alone. The Android app we're building will follow the same rule.
Why did the test in my browser stop?
A browser doesn't let us choose which connection to use. So during the test hiztesti.com checks that every connection comes from the same internet line. If some of them come from a different line (mobile data, for example), it stops the test straight away and shows the Test stopped message. The result isn't saved or shared.
You may also see this message on home or office networks that use two separate internet lines together. The reason is the same: the result wouldn't show the speed of a single connection.
How to turn it off
iPhone and iPad
Settings → Wi-Fi → turn off Connectivity Assist.
On older versions of iOS: Wi-Fi Assist at the bottom of Settings → Cellular (or Mobile Data).
Samsung Galaxy
Settings → Connections → Wi-Fi → ⋮ (top right) → Intelligent Wi-Fi → turn off Switch to mobile data.
Other Android phones
Open the Wi-Fi (or Network & internet) section in Settings and turn off the option called something like "switch to mobile data", "Wi-Fi assistant" or "smart network switch".
Menu names vary by phone brand and Android version.
You can turn the option back on after the test if you like.