def fake(cls, gsimlt=None):
        """
        :returns:
            a fake `CompositionInfo` instance with the given gsim logic tree
            object; if None, builds automatically a fake gsim logic tree
        """
        weight = 1
        gsim_lt = gsimlt or logictree.GsimLogicTree.from_('[FromFile]')
        fakeSM = logictree.LtSourceModel(
            'scenario', weight,  'b1',
            [sourceconverter.SourceGroup('*', eff_ruptures=1)],
            gsim_lt.get_num_paths(), ordinal=0, samples=1)
        return cls(gsim_lt, seed=0, num_samples=0, source_models=[fakeSM],
                   totweight=0)
:returns:
            a fake `CompositionInfo` instance with the given gsim logic tree
            object; if None, builds automatically a fake gsim logic tree