Requirements: composer 2.x should be used. Option 1: System composer Check if you have composer installed and its version " composer --version " If it is less than version 2, follow the Command-line installation instructions . Option 2: MDK If you use MDK, run `mdk phpunit` There should be a composer.phar file in your moodle root folder. Check version " php composer.phar --version " Optional: You can move it to the /usr/bin (" sudo mv composer.phar /usr/bin/composer ") so you can use the composer commands below as is. Otherwise, replace the " composer " commands below with " php composer.phar " The php version being used to run the composer commands below must be the lowest allowed for every branch (php72 for 39 and 310, php73 for 311 and master). Steps: Remove vendor & composer.lock: rm -fr vendor composer.lock Clear composer caches: composer clearcache Install: composer update Verify that a new composer.lock file has been created. Verify that it's the same (using git diff ) that the included in this patch (some minor versions / dates differences are allowed). Run vendor/bin/behat --version DON'T DO THIS!: Verify that "behat 3.10.0" is the version installed (this is a bug, they forgot to update the version constant to 3.10.0). ( link ). Open vendor/behat/behat/CHANGELOG.md Verify that you can see ## 3.10.0 - 2021-11-02 as the more recent (first) version. Apart from this, automated test will tell us if everything is ok.