Unions for engineers and conductors threaten a boycott of the tests that the agency and Amtrak, which takes over operation of the regional rail system July 1, plan to require. Engineers and conductors on Southern California's commuter rail service are threatening an en masse boycott of new personality-profiling tests required as a result of the 2008 Chatsworth disaster. The dispute sets up a potentially major labor-management clash just as the five-county Metrolink system is shifting to a new contractor to provide crews for trains that have nearly 1 million boardings a month. The screening tests, frequently used by corporate managers...