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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def AddAsMessage(self, rdfvalue_in, source, mutation_pool=None):
 """Helper method to add rdfvalues as GrrMessages for testing."""

    self.Add(
        rdf_flows.GrrMessage(payload=rdfvalue_in, source=source),
        mutation_pool=mutation_pool)