Initialise behat Run the following scenario: admin/tool/behat/tests/behat/keyboard.feature * Make a note of the approximate window size in your brain * (or take a screenshot) Open config.php and, just after the setting of behat_wwwroot set: $CFG->behat_window_size_modifier = 3; Run the scenario again Confirm that the window is 3 times larger (approximate guess is fine) Change the value to 0.5 Run the scenario again Confirm that the window is now half the original size (approximate guess is fine) Change the value to the string "oops"; Run the scenario again Confirm that the window is the original size Rejoice