To prevent 409 conflict on a primary node during ssyncing,
ssync-receiver should add x-ssync-backend-frag-index generated from
x-ssync-backend-node-index of the SSYNC replication request header.
The change is done by previous work[1], but we need more test for that.
This patch addes one more assertion if the x-ssync-backend-frag-index
is in the ssync subrequest correctly.
*BONUS*
Fix some weird mock and add some sanities.
1: https://review.openstack.org/#/c/191521/
Change-Id: I27aff713c69017c0bc4c60b4833184e1285595d7
81ceee056d