How to use the crds.getreferences function in crds

fits.writeto(readnoise_outfile, readnoise, overwrite=True)
            logging.info('\tReadnoise image saved to {}'.format(readnoise_outfile))

            # Calculate the full image readnoise stats
            clipped = sigma_clip(readnoise, sigma=3.0, maxiters=5)
            full_image_mean, full_image_stddev = np.nanmean(clipped), np.nanstd(clipped)
            full_image_n, full_image_bin_centers = self.make_histogram(readnoise)
            logging.info('\tReadnoise image stats: {:.5f} +/- {:.5f}'.format(full_image_mean, full_image_stddev))

            # Calculate readnoise stats in each amp separately
            amp_stats = self.get_amp_stats(readnoise, amp_bounds)
            logging.info('\tReadnoise image stats by amp: {}'.format(amp_stats))

            # Get the current JWST Readnoise Reference File data
            parameters = self.make_crds_parameter_dict()
            reffile_mapping = crds.getreferences(parameters, reftypes=['readnoise'])
            readnoise_file = reffile_mapping['readnoise']
            if 'NOT FOUND' in readnoise_file:
                logging.warning('\tNo pipeline readnoise reffile match for this file - assuming all zeros.')
                pipeline_readnoise = np.zeros(readnoise.shape)
            else:
                logging.info('\tPipeline readnoise reffile is {}'.format(readnoise_file))
                pipeline_readnoise = fits.getdata(readnoise_file)

            # Find the difference between the current readnoise image and the pipeline readnoise reffile, and record image stats.
            # Sometimes, the pipeline readnoise reffile needs to be cutout to match the subarray.
            pipeline_readnoise = pipeline_readnoise[self.substrt2-1:self.substrt2+self.subsize2-1, self.substrt1-1:self.substrt1+self.subsize1-1]
            readnoise_diff = readnoise - pipeline_readnoise
            clipped = sigma_clip(readnoise_diff, sigma=3.0, maxiters=5)
            diff_image_mean, diff_image_stddev = np.nanmean(clipped), np.nanstd(clipped)
            diff_image_n, diff_image_bin_centers = self.make_histogram(readnoise_diff)
            logging.info('\tReadnoise difference image stats: {:.5f} +/- {:.5f}'.format(diff_image_mean, diff_image_stddev))

of False is primarily intended to support testing on Travis.

    Returns
    -------

    reffile_mapping : dict
        Mapping of downloaded CRDS file locations
    """
    # IMPORTANT: Import of crds package must be done AFTER the environment
    # variables are set in the functions above
    import crds
    from crds import CrdsLookupError

    if download:
        try:
            reffile_mapping = crds.getreferences(parameter_dict, reftypes=reffile_types)
        except CrdsLookupError as e:
            raise ValueError("ERROR: CRDSLookupError when trying to find reference files for parameters: {}".format(parameter_dict))
    else:
        # If the files will not be downloaded, still return the same local
        # paths that are returned when the files are downloaded. Note that
        # this follows the directory structure currently assumed by CRDS.
        crds_path = os.environ.get('CRDS_PATH')
        try:
            reffile_mapping = crds.getrecommendations(parameter_dict, reftypes=reffile_types)
        except CrdsLookupError as e:
            raise ValueError("ERROR: CRDSLookupError when trying to find reference files for parameters: {}".format(parameter_dict))

        for key, value in reffile_mapping.items():
            # Check for NOT FOUND must be done here because the following
            # line will raise an exception if NOT FOUND is present
            if "NOT FOUND" in value: