def METHOD_NAME(specviz_helper, spectrum1d, uncert):
    if uncert is False:
        spectrum1d.uncertainty = None
    specviz_helper.load_data(spectrum1d, data_label="Test 1D Spectrum")
    viewer = specviz_helper.app.get_viewer("spectrum-viewer")
    plg = specviz_helper.plugins["Unit Conversion"]
    new_spectral_axis = "micron"
    plg.spectral_unit = new_spectral_axis
    assert len(specviz_helper.app.data_collection) == 1
    assert u.Unit(viewer.state.x_display_unit) == u.Unit(new_spectral_axis)
    assert u.Unit(viewer.state.y_display_unit) == u.Unit('Jy')