---
title: "Sentry Testkit"
description: "Learn how to assert that the right flow-tracking or error is being sent to Sentry, but without really sending it to the Sentry servers."
url: https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit/
---

# Sentry Testkit | Sentry for Fastify

When building tests for your application, you want to assert that the right flow-tracking or error is being sent to Sentry, but without really sending it to the Sentry servers. This way you won't swamp Sentry with false reports during test runs or other CI operations.

[Sentry Testkit](https://zivl.github.io/sentry-testkit/) is a community-maintained Sentry plugin that allows Sentry's reports to be intercepted for further data inspection. It enables Sentry to work natively in your application, by overriding Sentry's default transport mechanism, which makes it so that the report isn't really sent, but rather logged locally into memory. This way, logged reports can be fetched later for your own usage, verification, or any other purpose you may have in your local developing or testing environment.

Sentry Testkit is community-maintained and not officially supported by Sentry. Please open an issue in the [Sentry Testkit repository](https://zivl.github.io/sentry-testkit/) if you have any questions or feedback. Sentry makes no representations or warranties and disclaims all liability arising from, out of or in connection with the use of Sentry Testkit.

## [Installation](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#installation)

```bash
npm install sentry-testkit --save-dev
```

*Other available variations of the above snippet: yarn, pnpm*

Sentry Testkit supports the Sentry JavaScript SDK v8, v9, and v10. You don't need to change your test setup when upgrading across these SDK versions.

### [Using in tests](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#using-in-tests)

The simplest way to get started is to override Sentry's transport with `sentryTransport`, so the testkit captures events in memory instead of sending them to Sentry.

```javascript
import sentryTestkit from "sentry-testkit";

const { testkit, sentryTransport } = sentryTestkit();

// initialize your Sentry instance with sentryTransport
Sentry.init({
  dsn: "https://<key>@o<orgId>.ingest.sentry.io/<projectId>",
  transport: sentryTransport,
  //... other configurations
});

test("collect error events", function () {
  // run any scenario that eventually calls Sentry.captureException(...)
  expect(testkit.reports()).toHaveLength(1);
  const report = testkit.reports()[0];
  expect(report).toHaveProperty(/*...*/);
});

// Similarly for performance events
test("collect performance events", function () {
  // run any scenario that eventually calls Sentry.startTransaction(...)
  expect(testkit.transactions()).toHaveLength(1);
});
```

Reset the testkit between tests so captured data doesn't leak across cases:

```javascript
beforeEach(function () {
  testkit.reset();
});
```

You may see more usage examples in the [Sentry Testkit docs](https://zivl.github.io/sentry-testkit) as well.

### [What You Can Capture](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#what-you-can-capture)

Beyond errors and performance transactions, the testkit captures a range of Sentry event types:

* **Errors** — `testkit.reports()` returns all captured error reports. Each report also exposes any evaluated feature flags via `report.flags`.
* **Transactions** — `testkit.transactions()` returns all captured performance transactions.
* **Structured logs** — `testkit.logs()` returns captured logs (requires `enableLogs: true` in your Sentry configuration).
* **User feedback** — `testkit.feedback()` returns submitted user feedback.
* **Cron check-ins** — `testkit.checkIns()` returns cron monitor check-ins with their status.

The list keeps growing as Sentry adds new event types, so check the [Sentry Testkit docs](https://zivl.github.io/sentry-testkit) for the latest and more.

### [Finding and Filtering](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#finding-and-filtering)

* `testkit.findReport(error)` — locate a report by its `Error` object.
* `testkit.findReportByMessage(message)` — find a report by a string or `RegExp`.
* `testkit.findTransaction(name)` — locate a transaction by a string or `RegExp`.
* `testkit.reportsWithTag(key, value)` and `testkit.transactionsWithTag(key, value)` — filter by tag.
* `testkit.isExist(error)` — check whether an error was reported.

### [Waiting for Asynchronous Events](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#waiting-for-asynchronous-events)

Because Sentry reports events asynchronously, the testkit provides awaitable helpers that resolve once the expected number of items has been captured (or a timeout is reached): `waitForReports`, `waitForTransactions`, `waitForLogs`, `waitForFeedback`, and `waitForCheckIns`.

```javascript
test("collect error events", async function () {
  // run any scenario that eventually calls Sentry.captureException(...)
  const reports = await testkit.waitForReports(1, { timeout: 1000 });
  expect(reports).toHaveLength(1);
});
```

### [Network Interception](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#network-interception)

If you can't (or don't want to) override the transport — for example in end-to-end tests — you can intercept Sentry's network requests instead, without changing your application's `Sentry.init` configuration. `initNetworkInterceptor` works with your interception library of choice (such as `nock`) and parses every item of an envelope, capturing all supported event types.

This makes the testkit suitable for setups ranging from unit tests to E2E environments, including Puppeteer, Playwright, browser-only, and React Native.

### [Testkit API](https://docs.sentry.io/platforms/javascript/guides/fastify/best-practices/sentry-testkit.md#testkit-api)

See the full API description and documentation in the [Sentry Testkit Docs](https://zivl.github.io/sentry-testkit/docs/api).