async-ordering-tests

Async ordering bugs ("user A's update overwrote user B's" / "callback fired twice" / "promise resolved before fetch returned") look like race conditions but operate at the runtime level (event loop / scheduler). Tests must control the scheduler to be deterministic.

When to use

• UI updates that depend on multiple in-flight requests resolving in the right order.
• Server-side: parallel I/O whose completion order affects the final state.
• Callback-heavy code where re-entrancy (sync vs async dispatch) matters.

Step 1 - JS Promise microtask vs macrotask