mongo/jstests/core/regex_options.js

t = db.jstests_regex_options;

t.drop();
t.save({a: "foo"});
assert.eq(1, t.count({a: {"$regex": /O/i}}));
assert.eq(1, t.count({a: /O/i}));
assert.eq(1, t.count({a: {"$regex": "O", "$options": "i"}}));