Currently to assert that a given Metric<Distribution> as a certain distribution for some labels, the caller needs to manually create an ImmutableDistribution and pass it to #hasValueForLabels method. With this change, an ImmutableSet of data points can be passed to #hasDataSetForLabels method.
Also switched to use expectThrow backport from JUnit 4.13.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=173544521