t = db["jstests_coveredIndex2"];
t.drop();

// Include helpers for analyzing explain output.
load("jstests/libs/analyze_plan.js");

t.save({a: 1})
t.save({a: 2})
assert.eq( t.findOne({a: 1}).a, 1, "Cannot find right record" );
assert.eq( t.count(), 2, "Not right length" );

// use simple index
t.ensureIndex({a: 1});
var plan = t.find({a:1}).explain();
assert( !isIndexOnly(plan.queryPlanner.winningPlan),
        "Find using covered index but all fields are returned");
var plan = t.find({a:1}, {a: 1}).explain();
assert( !isIndexOnly(plan.queryPlanner.winningPlan),
        "Find using covered index but _id is returned");
var plan = t.find({a:1}, {a: 1, _id: 0}).explain();
assert( isIndexOnly(plan.queryPlanner.winningPlan),
        "Find is not using covered index");

// add multikey
t.save({a:[3,4]})
var plan = t.find({a:1}, {a: 1, _id: 0}).explain();
assert( !isIndexOnly(plan.queryPlanner.winningPlan),
        "Find is using covered index even after multikey insert");