mongo/jstests/core/query/update/update_arraymatch1.js

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

let o = {
    _id: 1,
    a: [
        {x: 1, y: 1},
        {x: 2, y: 2},
        {x: 3, y: 3},
    ],
};
assert.commandWorked(t.insert(o));
assert.eq(o, t.findOne(), "A1");

let q = {"a.x": 2};
assert.commandWorked(t.update(q, {$set: {b: 5}}));
o.b = 5;
assert.eq(o, t.findOne(), "A2");

assert.commandWorked(t.update({"a.x": 2}, {$inc: {"a.$.y": 1}}));
o.a[1].y++;
assert.eq(o, t.findOne(), "A3");