def test_layers_view():
    X = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
    L = np.array([[10, 11, 12], [13, 14, 15], [16, 17, 18]])
    real_adata = ad.AnnData(X)
    real_adata.layers["L"] = L
    view_adata = real_adata[1:, 1:]
    real_hash = joblib.hash(real_adata)
    view_hash = joblib.hash(view_adata)

    assert view_adata.is_view

    with pytest.raises(ValueError):
        view_adata.layers["L2"] = L + 2

    assert view_adata.is_view  # Failing to set layer item makes adata not view
    assert real_hash == joblib.hash(real_adata)
    assert view_hash == joblib.hash(view_adata)

    view_adata.layers["L2"] = L[1:, 1:] + 2

    assert not view_adata.is_view
    assert real_hash == joblib.hash(real_adata)
    assert view_hash != joblib.hash(view_adata)
def reset_interactive_output_stream(
        cls, interactive_output_stream, override_faulthandler_destination=True
    ):
        """Class state:

        - Overwrites `cls._interactive_output_stream`.
        OS state:
        - Overwrites the SIGUSR2 handler.

        This method registers a SIGUSR2 handler, which permits a non-fatal `kill -31 <pants pid>` for
        stacktrace retrieval. This is also where the the error message on fatal exit will be printed to.
        """
        try:
            # NB: mutate process-global state!
            # This permits a non-fatal `kill -31 <pants pid>` for stacktrace retrieval.
            if override_faulthandler_destination:
                faulthandler.register(
                    signal.SIGUSR2, interactive_output_stream, all_threads=True, chain=False
                )
            # NB: mutate the class variables!
            cls._interactive_output_stream = interactive_output_stream
        except ValueError:
            # Warn about "ValueError: IO on closed file" when the stream is closed.
            cls.log_exception(
                "Cannot reset interactive_output_stream -- stream (probably stderr) is closed"
            )