def METHOD_NAME(cls, values: dict) -> None:
    """Check that a logo exists for each source and vice versa."""
    logos_path = pathlib.Path(__file__).parent.parent / "logos"
    for source_type in values:
        logo_path = logos_path / f"{source_type}.png"
        if not logo_path.exists():
            msg = f"No logo exists for {source_type}"
            raise ValueError(msg)
    for logo_path in logos_path.glob("*.png"):
        if logo_path.stem not in values:
            msg = f"No source exists for {logo_path}"
            raise ValueError(msg)