code: def populateFromDirectory(self, vcfDirectory):
          
          pattern = os.path.join(vcfDirectory, "*.vcf.gz")
          dataFiles = []
          indexFiles = []
          for vcfFile in glob.glob(pattern):
              dataFiles.append(vcfFile)
              indexFiles.append(vcfFile + ".tbi")
          self.populateFromFile(dataFiles, indexFiles)
docs: Populates this VariantSet by examing all the VCF files in the
          specified directory. This is mainly used for as a convenience
          for testing purposes.