Tracking Testing

Broken tracking does not throw. Nothing turns red. The product works perfectly and the business spends a month optimising against numbers that were never real — and by the time someone notices, the data for that month cannot be recovered.

For a company that buys traffic, this is not a nice-to-have: a conversion event that stops firing silently teaches the ad platform to optimise for the wrong people.

Assert on the request, not on the console

The only trustworthy oracle is the network call that leaves the browser:

const hits = []
await page.route('**/*', route => {
  const u = route.request().url()
  if (/google-analytics|analytics\.google|facebook\.com\/tr|googletagmanager/.test(u)) {
    hits.push({ url: u, body: route.request().postData(), method: route.request().method() })
  }
  route.continue()
})

await checkout(page)
const purchase = hits.find(h => /(\ben=purchase\b|"event":"purchase"|ev=Purchase)/.test(h.url + h.body))
expect(purchase, 'purchase event never left the browser').toBeTruthy()

Then assert the payload, not just that something fired: value, currency, transaction id, items, and the user/consent identifiers. A purchase with no value is worse than no event — it looks correct in the tag debugger and reports zero revenue.

The event contract

Write the contract once, generate the tests from it (state-machine-testing style), and keep it next to the code:

The two rows that cost the most money: purchase on a declined payment (inflates conversions, poisons the ad platform's model) and duplicate purchase on refresh (same, doubled). Test both by name.

Deduplication and server-side

When the same conversion is sent from browser and server (Meta CAPI, GA4 Measurement Protocol), both must carry the same event_id — otherwise every conversion is counted twice. Assert the id matches across the two payloads in one test; nothing else catches this.

Consent

• Before consent: no tracking request leaves at all. Assert zero matching hits, not "a hit with anonymised data".
• After accept: events fire, with consent flags set.
• After reject: still zero, and still zero after a reload — the classic bug is consent that resets.

This is also compliance: LGPD and GDPR make an ungated pixel a legal exposure, not just a data quality problem.

Guard against silent death

Tracking breaks by disappearing. Add a synthetic check that runs the money journey daily against production and fails when the purchase request stops arriving. A test that only runs in CI cannot catch a tag manager change someone made in a web console at 4pm on a Friday.

Done means

Per event: fired / not fired, payload asserted field by field, consent states covered, and the dedup id proven identical across browser and server.