def METHOD_NAME(self, _mk_checkSourceReplicas):
    """Suppose they all go to the same target"""
    fts3Plugin = DefaultFTS3Plugin()
    res = selectUniqueSource(self.allFiles, fts3Plugin)
    self.assertTrue(res["OK"])
    uniqueSources, _failedFiles = res["Value"]
    # There should be only f1,f2 and f3
    allReturnedFiles = []
    existingFiles = [self.f1, self.f2, self.f3]
    for _srcSe, ftsFiles in uniqueSources.items():
        allReturnedFiles.extend(ftsFiles)
    # No files should be duplicated and all files should be there, except the non existing one
    self.assertEqual(len(existingFiles), len(allReturnedFiles))
    self.assertEqual(set(existingFiles), set(allReturnedFiles))
    filesInSrc1 = uniqueSources.get("Src1", [])
    filesInSrc2 = uniqueSources.get("Src2", [])
    filesInSrc3 = uniqueSources.get("Src3", [])
    filesInSrc4 = uniqueSources.get("Src4", [])
    # f1
    self.assertTrue(self.f1 in filesInSrc1 + filesInSrc2)
    self.assertTrue(self.f2 in filesInSrc2 + filesInSrc3)
    self.assertTrue(self.f3 in filesInSrc4)