let res;
const t = db[jsTestName()];
t.drop();

function doTest() {
    assert.commandWorked(
        t.save({
            a: [
                {id: 1, x: [5, 6, 7]},
                {id: 2, x: [8, 9, 10]},
            ],
        }),
    );
    assert.commandWorked(t.update({"a.id": 1}, {$set: {"a.$.x": [1, 1, 1]}}));
    assert.eq(1, t.findOne().a[0].x[0]);
}

doTest();
assert(t.drop());
assert.commandWorked(t.createIndex({"a.id": 1}));
doTest();