PHOENIX — Bud Black tosses out baseball truisms almost daily. “That’s baseball,” the Rockies manager loves to say about the quirks of the grand old game. Here’s another favorite: “Every day is a test.” For a Rockies’ offense that struggled to find its identity and produce some power last season, the test began Thursday night in the season-opener against Arizona right-hander Zac Gallen, one of the best pitchers in the majors.