Runs tests to ensure that antikythera's upgrade doesn't break backward-compatibility.

It works in the following sequence:

• Starts an antikythera instance of a version specified by a git ref, with gears in specified directories installed
• (If testgear is used, establishes websocket connection to testgear. Periodically sends echo requests)
• Upgrades the antikythera instance to new version specified by another git ref
• Run blackbox tests defined in each gear, checking whether their external behaviors are kept intact
• (Raises if the websocket connection established above was abnormally closed before here)

Usage

$ mix antikythera_local.upgrade_compatibility_test <comma_separated_gear_directories> [git_ref_from[ git_ref_to]]

• comma_separated_gear_directories can be absolute or relative paths to directories, such as ../testgear,/path/to/another_gear.
  • It assumes basenames of paths exactly match gear_names, for testgear detection.
• git_ref_from defaults to HEAD^. git_ref_to defaults to HEAD.