test(browser:) Add test about re-sampling new traces (#16730)

mydea · s1gr1d · web-flow · commit 293049904668 · 2025-06-25T11:04:34.000Z
Adding a test for a support case, to ensure that new trace are correctly
sampled.

---------

Co-authored-by: Sigrid Huemer &lt;32902192+s1gr1d@users.noreply.github.com&gt;
diff --git a/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/init.js b/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/init.js
@@ -0,0 +1,19 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+// Force this so that the initial sampleRand is consistent
+Math.random = () => 0.45;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  integrations: [Sentry.browserTracingIntegration()],
+  tracePropagationTargets: ['http://sentry-test-site.example'],
+  tracesSampler: ({ name }) => {
+    if (name === 'new-trace') {
+      return 0.9;
+    }
+
+    return 0.5;
+  },
+});
diff --git a/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/subject.js b/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/subject.js
@@ -0,0 +1,13 @@
+const newTraceBtn = document.getElementById('newTrace');
+newTraceBtn.addEventListener('click', async () => {
+  Sentry.startNewTrace(() => {
+    // We want to ensure the new trace is sampled, so we force the sample_rand to a value above 0.9
+    Sentry.getCurrentScope().setPropagationContext({
+      ...Sentry.getCurrentScope().getPropagationContext(),
+      sampleRand: 0.85,
+    });
+    Sentry.startSpan({ op: 'ui.interaction.click', name: 'new-trace' }, async () => {
+      await fetch('http://sentry-test-site.example');
+    });
+  });
+});
diff --git a/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/template.html b/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/template.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+  </head>
+  <body>
+    <button id="newTrace">new Trace</button>
+  </body>
+</html>
diff --git a/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/test.ts b/dev-packages/browser-integration-tests/suites/tracing/trace-lifetime/startNewTraceSampling/test.ts
@@ -0,0 +1,89 @@
+import { expect } from '@playwright/test';
+import { sentryTest } from '../../../../utils/fixtures';
+import type { EventAndTraceHeader } from '../../../../utils/helpers';
+import {
+  eventAndTraceHeaderRequestParser,
+  getFirstSentryEnvelopeRequest,
+  shouldSkipTracingTest,
+  waitForTransactionRequest,
+} from '../../../../utils/helpers';
+
+sentryTest(
+  'new trace started with `startNewTrace` is sampled according to the `tracesSampler`',
+  async ({ getLocalTestUrl, page }) => {
+    if (shouldSkipTracingTest()) {
+      sentryTest.skip();
+    }
+
+    const url = await getLocalTestUrl({ testDir: __dirname });
+
+    await page.route('http://sentry-test-site.example/**', route => {
+      return route.fulfill({
+        status: 200,
+        contentType: 'application/json',
+        body: JSON.stringify({}),
+      });
+    });
+
+    const [pageloadEvent, pageloadTraceHeaders] = await getFirstSentryEnvelopeRequest<EventAndTraceHeader>(
+      page,
+      url,
+      eventAndTraceHeaderRequestParser,
+    );
+
+    const pageloadTraceContext = pageloadEvent.contexts?.trace;
+
+    expect(pageloadEvent.type).toEqual('transaction');
+
+    expect(pageloadTraceContext).toMatchObject({
+      op: 'pageload',
+      trace_id: expect.stringMatching(/^[0-9a-f]{32}$/),
+      span_id: expect.stringMatching(/^[0-9a-f]{16}$/),
+      data: {
+        'sentry.sample_rate': 0.5,
+      },
+    });
+    expect(pageloadTraceContext).not.toHaveProperty('parent_span_id');
+
+    expect(pageloadTraceHeaders).toEqual({
+      environment: 'production',
+      public_key: 'public',
+      sample_rate: '0.5',
+      sampled: 'true',
+      trace_id: pageloadTraceContext?.trace_id,
+      sample_rand: '0.45',
+    });
+
+    const transactionPromise = waitForTransactionRequest(page, event => {
+      return event.transaction === 'new-trace';
+    });
+
+    await page.locator('#newTrace').click();
+
+    const [newTraceTransactionEvent, newTraceTransactionTraceHeaders] = eventAndTraceHeaderRequestParser(
+      await transactionPromise,
+    );
+
+    const newTraceTransactionTraceContext = newTraceTransactionEvent.contexts?.trace;
+    expect(newTraceTransactionTraceContext).toMatchObject({
+      op: 'ui.interaction.click',
+      trace_id: expect.stringMatching(/^[0-9a-f]{32}$/),
+      span_id: expect.stringMatching(/^[0-9a-f]{16}$/),
+      data: {
+        'sentry.sample_rate': 0.9,
+      },
+    });
+
+    expect(newTraceTransactionTraceHeaders).toEqual({
+      environment: 'production',
+      public_key: 'public',
+      sample_rate: '0.9',
+      sampled: 'true',
+      trace_id: newTraceTransactionTraceContext?.trace_id,
+      transaction: 'new-trace',
+      sample_rand: '0.85',
+    });
+
+    expect(newTraceTransactionTraceContext?.trace_id).not.toEqual(pageloadTraceContext?.trace_id);
+  },
+);
