https://www.reuters.com/article/tesla-musk-rivian/musk-says-high-production-breakeven-cash-flow-true-test-for-rivian-idUSKBN2HW2PR >Tesla Inc boss Elon Musk said on Thursday high production and breakeven cash flow would be the "true test" for Rivian Automotive Inc, a day after the electric vehicle maker's blockbuster market debut.