FTR: The test fails, because the dtype of the metadata array in the test file changes during the read/write cycle in the test. The actual content is unchanges though.
After initial write: array([['dt', '0.1'], ['first_id', '0'], ['first_index', '0'], ['label', 'population0'], ['last_id', '4'], ['last_index', '5'], ['n', '505'], ['size', '5'], ['units', 'mV'], ['variable', 'v']], dtype='|S11') and after the re-write: array([['dt', '0.1'], ['first_id', '0'], ['first_index', '0'], ['label', 'population0'], ['last_id', '4'], ['last_index', '5'], ['n', '505'], ['size', '5'], ['units', 'mV'], ['variable', 'v']], dtype='|S32') Not yet clear on how this happens. ttfn