Thanks! I think it would be a bit better to move the call to self.base_workdir.mkdir() in build() up above the call to createrepo.

build() doesn't reference self.base_workdir until after the current mkdir() call (since self.mock_cfg_path is defined relative to self.base_workdir). createrepo does explicitly reference self.base_workdir, hence this patch. It is not clear to me the relationship between self.base_workdir and self.repo_path. Furthermore, this makes createrepo self-containing, as not every caller needs to remember to mkdir before calling it first.

build() is the wrapper function around the whole build process - build_item() and createrepo() can only occur within build().

So, what I'd expect is

    def build(self):
        self.base_workdir.mkdir(parents=True, exist_ok=True)
        # The repo will be referenced in the mock config, since it
        # is a build-requirements source as well as a destination,
        # so we need to make sure it valid before we start building
        if not (self.repo_path / "repodata/repomd.xml").exists():
            asyncio.run(self.createrepo())
        with open(self.mock_cfg_path, "w") as f:
            f.write(self.mock_cfg)
        super().build()

and from my perspective, i just added the createrepo() call in the wrong place. If the call to self.base_workdir.mkdir() was specific to self.mock_cfg_path, I would have written: self.mock_cfg_path.parent.mkdir()

Of course, it doesn't really matter... your patch would work fine.

Merging, doesn't really matter. Thanks for the patch!