`./mach test --all` passes incorrect number of arguments to test-tidy

[warren-fisher]

On Ubuntu 19.10, ./mach test --all fails on the current master branch with:

Error running mach:

    ['test', '--all']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.
You can invoke |./mach busted| to check if this issue is already on file. If it
isn't, please use |./mach busted file| to report it. If |./mach busted| is
misbehaving, you can also inspect the dependencies of bug 1543241.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

TypeError: test_tidy() takes exactly 7 arguments (5 given)

  File "/home/warren/programming/servo/python/servo/testing_commands.py", line 176, in test
    Registrar.dispatch("test-%s" % suite, context=self.context, **kwargs)
  File "/home/warren/programming/servo/python/_virtualenv2.7/lib/python2.7/site-packages/mach/registrar.py", line 152, in dispatch
    return self._run_command_handler(handler, context=context, **kwargs)
  File "/home/warren/programming/servo/python/_virtualenv2.7/lib/python2.7/site-packages/mach/registrar.py", line 109, in _run_command_handler
    result = fn(**kwargs)

#16071 seems related. The main file in question is python/servo/testing_commands.py.

Running ./mach test-tidy --self-test succeeds with all 29 tests passing.

Running ./mach test --all --self-test or ./mach test tidy --self-test fail with the same error as ./mach test --all. Perhaps --self-test was never meant to work with either of these options, I am not sure.

[warren-fisher]

After further testing (adding a print statement on line 175 of python/servo/testing_commands the following dictionary is passed to test_tidy() in python/servo/testing_commands.py as keyword arguments:
{u'all_files': False, u'self_test': True, u'no_progress': False, u'stylo': False}

As can be seen the no_wpt and force_cpp arguments are not being provided. However using ./mach test-tidy these are passed using the @CommandArgument decorators default value. Perhaps it would be best to set no_wpt and force_cpp to have defaults of False in the function signature. This should allow for ./mach test --all to correctly identify the default values intended by the @CommandArgument decorator without have to change anything else.

Testing this on my local machine did fix the problem. Will submit a PR tonight.