The jstests/core/txns directory is intended to contain transactions tests that are topology agnostic i.e. tests that would generalize from a single replica set to a sharded cluster. Tests that run 'prepareTransaction' are not topology agnostic i.e. they depend on the fact that they are run against a single replica set, not a mongos. As a consequence of this, any test that runs prepareTransaction and is placed inside jstests/core/txns must then be blacklisted from any sharded transaction suite, e.g. sharded_core_txns. This blacklisting effort is unnecessary since we would never intend to run these tests in sharded passthroughs since the functionality they test is specific to single replica sets. Placing them in jstests/replsets obviates the need to do any blacklisting. Ideally we would move all existing "prepare" tests in jstests/core/txns into jstests/replsets.