mongo/jstests/core/query/set/set1.js

let t = db.set1;
t.drop();

t.insert({_id: 1, emb: {}});
t.update({_id: 1}, {$set: {emb: {"a.dot": "data"}}});
assert.eq({_id: 1, emb: {"a.dot": "data"}}, t.findOne(), "A");