Currently, sharding_jscore_passthrough runs sharded clusters as standalone shards by default.
As a result, write_result.js also expects the same. Since this test is only run against sharded clusters with standalone shards, we can expect replSet to only be true if it is communicating with the replica set directly. Therefore, this test fails on multiversion tests that run against sharded clusters with replica set shards.
SERVER-43892 and once we can expect the sharding core passthroughs to start shards as replica sets by default, we can re-enable this test for multiversion testing.