Change tests option from --watch to --live to avoid node conflict

[lyzadanger]

Node 18.11 introduced a core --watch flag. This creates a conflict with using a --watch option in the tests task module. For now, change the name of the task's option to --live to avoid this conflict.

Updated usage:

gulp test --live

Testing this change

• In the main branch of the client, with a local node version of >=18.11, try running gulp test --watch. It should fail.
• Check out this branch of frontend-build. Run yalc publish
• In the client directory, run yalc add @hypothesis/frontend-build
• In the client, run gulp test --live. It should work: tests should run and then run again on input/source file changes

[lyzadanger]

In the course of poking at this, I noticed that https://h.readthedocs.io/projects/client/en/latest/developers/developing.html 's section on testing is fairly egregiously out-of-date. We should update that documentation after we sort this.

[acelaya]

👍🏼

[robertknight]

After doing some digging, it looks like the issue is that the --watch flag matches a V8 flag which is detected by the flagged-respawn package that Gulp uses internally. According to the npm README, flagged-respawn respects a --no-respawning flag to disable its behavior. This almost works:

gulp test --watch --no-respawning

Except that the runTests function in @hypothesis/frontend-build complains about not understanding the --no-respawning flag. With a slight modification to the CLI arg parsing, the above command works:

  // Parse command-line options for test execution.
  program
    .option(
      '--grep <pattern>',
      'Run only tests where filename matches a regex pattern'
    )
    .option('--watch', 'Continuously run tests (default: false)', false)
    .parse(process.argv.filter(a => a !== '--no-respawning'));

This is why various other tools that have a --watch flag continue to work in the latest version of Node: they don't use gulp. Normally the Node-specific (as opposed to tool-specific) --watch flag would only be handled when the flag comes before the script name in the command:

node --watch path/to/tool --watch

In the above the first --watch is for Node, the second --watch is for the tool.

[robertknight]

To recap, the issue here is that Gulp is detecting any Node or V8 flag names in the CLI args and doing unwanted things if it sees them. The problem arose after a Node update because --watch is now a recognized Node/V8 flag name, according to the v8flags package. There is a way to turn this behavior off, but it is cumbersome.

I would prefer to use --watch as a more obvious name than --live, but as long as we're still using gulp, then the dumb approach of avoiding flag names that conflict with Node/V8 flags is the easiest thing to do. If we migrate away from gulp in future, we can revert the name to --watch.