Add unittests for ingestion stale NaNs
Add unittests for ingestion stale NaNs

yanghongkjxy/prometheus,amorken/prometheus,alileza/prometheus,brancz/prometheus,kangwoo/prometheus,kangwoo/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,prometheus/prometheus,AlekSi/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,Conorbro/prometheus,Gouthamve/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,kangwoo/prometheus,brancz/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,AlekSi/prometheus,AlekSi/prometheus,Conorbro/prometheus,alileza/prometheus,brancz/prometheus,Gouthamve/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,brancz/prometheus,keegancsmith/prometheus,Conorbro/prometheus,GoogleCloudPlatform/prometheus,yanghongkjxy/prometheus,AlekSi/prometheus,amorken/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,alileza/prometheus,prometheus/prometheus,alileza/prometheus,Conorbro/prometheus,keegancsmith/prometheus,amorken/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus,prometheus/prometheus,amorken/prometheus