Failed to run ./mach mochitest --tag on my MacOS 10.14. Based on m-c changeset (561070:b47b9a46d5f7), which is the version on Oct 13th.

➜  mozilla-central ./mach mochitest --tag audiochannel
Error running mach:

    ['mochitest', '--tag', 'audiochannel']

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 mochitest| 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: keys must be str, int, float, bool or None, not bytes

  File "/Users/awu/gecko-dev/mozilla-central/testing/mochitest/mach_commands.py", line 327, in run_mochitest_general
    tests = mochitest.resolve_tests(test_paths, test_objects, cwd=self._mach_context.cwd)
  File "/Users/awu/gecko-dev/mozilla-central/testing/mochitest/mach_commands.py", line 98, in resolve_tests
    tests = list(resolver.resolve_tests(paths=test_paths, cwd=cwd))
  File "/Users/awu/gecko-dev/mozilla-central/testing/mozbase/moztest/moztest/resolve.py", line 857, in resolve_tests
    for test in self._resolve(**kwargs):
  File "/Users/awu/gecko-dev/mozilla-central/testing/mozbase/moztest/moztest/resolve.py", line 622, in _resolve
    self.add_wpt_manifest_data()
  File "/Users/awu/gecko-dev/mozilla-central/testing/mozbase/moztest/moztest/resolve.py", line 753, in add_wpt_manifest_data
    manifests = manifestupdate.run(self.topsrcdir, self.topobjdir, rebuild=False,
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/manifestupdate.py", line 119, in run
    manifests = load_and_update(logger, src_wpt_dir, test_paths,
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/manifestupdate.py", line 188, in load_and_update
    m = manifest.manifest.load_and_update(paths["tests_path"],
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/tests/tools/manifest/manifest.py", line 398, in load_and_update
    return _load_and_update(ensure_text(tests_root),
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/tests/tools/manifest/manifest.py", line 466, in _load_and_update
    tree.dump_caches()
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/tests/tools/manifest/vcs.py", line 130, in dump_caches
    cache.dump()
  File "/Users/awu/gecko-dev/mozilla-central/testing/web-platform/tests/tools/manifest/vcs.py", line 153, in dump
    json.dump(self.data, f, indent=1)
  File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/__init__.py", line 179, in dump
    for chunk in iterable:
  File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/json/encoder.py", line 376, in _iterencode_dict
    raise TypeError(f'keys must be str, int, float, bool or None, '

I cannot reproduce: './mach mochitest --tag audiochannel' works for me, on Ubuntu.

As I recall, :bc had a similar problem a few weeks ago?

:jgraham might have insight into the wpt manifest update?

I believe this fails when loading files from ~/.mozbuild/cache/wpt -- I wonder if deleting ~/.mozbuild/cache/wpt would help?

Yeah, it looks like there might be a corrupt cache there. Try deleting as gbrown suggests.

(In reply to Geoff Brown [:gbrown] from comment #1)

I believe this fails when loading files from ~/.mozbuild/cache/wpt -- I wonder if deleting ~/.mozbuild/cache/wpt would help?

Thank you so much, it works well for me!