Right now we get some test coverage for this from index tests that run in the tenant_migration_jscore_passthrough suite if the background migration happens to conflict with the commitIndexBuild oplog entry but there is no test that explicitly tests for this. The test case for createIndex in tenant_migration_concurrent_writes.js always runs createIndex after the migration has entered the write blocking state so TenantMigrationConflict is thrown when we try to write the startIndexBuild oplog entry as supposed to the commitIndexBuild oplog entry .