Comment 14 for bug 1828929

I also had this problem.

Following the instructions on the official website it works.

Go here: https://www.speedtest.net/apps/cli

First, remove actual speedtest if installed.

Follow the official instructions:
sudo apt-get install gnupg1 apt-transport-https dirmngr
export INSTALL_KEY=379CE192D401AB61
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys $INSTALL_KEY
echo "deb https://ookla.bintray.com/debian generic main" | sudo tee /etc/apt/sources.list.d/speedtest.list
sudo apt-get update
# Other non-official binaries will conflict with Speedtest CLI
# Example how to remove using apt-get
# sudo apt-get remove speedtest-cli
sudo apt-get install speedtest

Run speedtest