Simplify TestHeadReadWriter_Truncate (#7437)
Simplify TestHeadReadWriter_Truncate (#7437)

* Simplify TestHeadReadWriter_Truncate

Signed-off-by: Ganesh Vernekar <cb5593e95c6f4f9d31a7d363cec8452e89af4967@iith.ac.in>

* Fix review comments

Signed-off-by: Ganesh Vernekar <cb5593e95c6f4f9d31a7d363cec8452e89af4967@iith.ac.in>
prometheus/prometheus,alileza/prometheus,prometheus/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,alileza/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,alileza/prometheus,prometheus/prometheus