Freeze time in a test

Javascript

Node's mock timers make anything date-dependent deterministic without injecting a clock everywhere.

import { mock, test } from 'node:test';

test('expires after an hour', (t) => {
  t.mock.timers.enable({ apis: ['Date'], now: new Date('2026-01-01T00:00:00Z') });
  const token = issueToken();
  t.mock.timers.tick(61 * 60 * 1000);
  assert.equal(isValid(token), false);
});

Download

Testing testing time mocking chris

More in Testing

A test that fails for the right reason Testing Assert on the message, not merely that something threw. A typo raising TypeError would otherwise pass. Table-driven tests in Go Testing The idiomatic Go pattern: a slice of cases and a subtest per entry, each named so failures are readable. Parameterised tests in Python Testing One test body, many cases, and a failure that names the case that broke.

Random picks

Safe navigation and fetch in Ruby Ruby &. stops at nil; fetch raises rather than returning nil when a key is genuinely required. Reset a Postgres sequence after a bulk import Databases Copying rows with explicit ids leaves the identity sequence behind, so the next insert collides with an existing row. Add a column without locking the table Databases On Postgres 11 and later a nullable column with a default is a metadata-only change. Adding NOT NULL afterwards is the part that needs care. Watch a command until it succeeds Shell Retries every two seconds and stops the moment the command exits zero. Useful while waiting for a service to come up. Relative time without a date library JavaScript Turns a timestamp into 'three days ago' using the built-in formatter. Merge dictionaries Python The | operator returns a new dict; |= updates in place. Later keys win in both. Worker pool with a wait group in Go Systems Fixed number of goroutines draining a channel, with the group ensuring main waits for all of them. Make some properties optional TypeScript Composes the built-in helpers rather than writing a second interface that will drift from the first.