def METHOD_NAME() -> MatrixService:
    """
    Fixture for creating a mocked matrix service.
    Returns:
        An instance of the `SimpleMatrixService` class representing the matrix service.
    """
    def create(data):
        """
        This function calculates a unique ID for each matrix, without storing
        any data in the file system or the database.
        """
        matrix = data if isinstance(data, np.ndarray) else np.array(data, dtype=np.float64)
        matrix_hash = hashlib.sha256(matrix.data).hexdigest()
        return matrix_hash
    matrix_service = Mock(spec=MatrixService)
    matrix_service.create.side_effect = create
    return matrix_service