The current production version of mtail doesn't support histograms in -oneshot mode, thus making it impossible to use our current testing framework:
$ mtail -one_shot -logtostderr -progs mediawiki_access_log.mtail -logs ../test/logs/mediawiki_access_log.test [CUT] Metrics store:E0924 11:18:13.353454 81132 main.go:178] failed to marshal metrics into json: json: unsupported value: +Inf
This happens because json marshalling automatically assumes the bucket field of the map to be an integer, and "+Inf" isn't an integer. See https://github.com/google/mtail/issues/223
The fix is pretty simple https://github.com/google/mtail/commit/4e8b829b9333346fc82c8a5ee253c07c8a87e105 and is included in mtail 3.0.0-rc36 AFAICT.
The work on the API gateway SLOs (T254916) is blocked on us either backporting that single fix or moving to mtail 3.0.0-rc36.