The passthrough suite sharded_collections_causally_consistent_jscore_txns_passthrough is meant to test causal consistency doesn't interfere with the basic txn tests in jscore/txns, but doesn't actually load an override to enable causal consistency. This suite should load "jstests/libs/override_methods/enable_causal_consistency_without_read_pref.js" like sharded_causally_consistent_jscore_txns_passthrough.