Migrate example tests for Web Test Runner by matux · Pull Request #1298 · rollbar/rollbar.js

matux · 2025-09-04T14:26:39Z

Caution

This PR is being merged into a feature branch: matux/wtr.

Note

Multiple comments in the diff with details/reasoning about specific changes.

Description of the change

This PR completes the migration of example tests from Karma to Web Test Runner, fixing critical issues with loading HTML fixtures and handling uncaught errors.

New Test Utilities

test/util/fixtures.js: Added loadHtml helper to load HTML fixtures in a WTR/Playwright-friendly way with proper script handling
- Handles both inline and external scripts
- Preserves script type to prevent module/classic script conflicts in WTR
test/util/timers.js: Added promise-based setTimeout to avoid cases where both await and done were needed (which is illegal).

Migrated Example Tests

test/examples/react.test.js: Migrated React example test with proper uncaught error handling
test/examples/universalBrowser.test.js: Migrated universal browser test
test/examples/universalBrowserConfig.test.js: Migrated universal browser config test
test/examples/webpack.test.js: Migrated webpack example test

Fixes

Fixed script loading issues by preserving type attribute to prevent WTR from treating classic scripts as ES modules
Handled uncaught error testing by temporarily disabling Mocha's error handler
Updated HTML fixtures to work with WTR's static file serving

Test Results

All 369 tests passing
Example tests now fully integrated with Web Test Runner
Removed dependency on Karma's html fixture loading

Technical Notes

The main two challenges were

WTR/Mocha installs a window.onerror handler that fails tests on any uncaught error. This conflicted with tests verifying Rollbar's error catching. Solution: temporarily disable Mocha's handler during these tests, allowing Rollbar to catch errors without WTR interference.
handling the difference between how Karma and WTR load HTML fixtures and handle scripts. WTR defaults to treating dynamically created scripts as ES modules, which broke bundled classic scripts. The solution was to preserve the original type attribute when recreating script elements.

Related issues

SDK-493/replace-karma-with-webtest-runner-for-modern-performant-browser

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matux · 2025-09-04T14:40:36Z

    <script>
-      var domainsBlocked = ['localhost'];
-
-      function ignoreFilesUncaught(isUncaught, args, payload) {
-        try {
-          var filename = payload.data.body.trace.frames[0].filename;
-
-          var isBlocked = domainsBlocked.some(function (domain) {
-            return filename.indexOf(domain) !== -1;
-          });
-
-          if (isUncaught && isBlocked) {
-            console.log('Ignoring error from ' + filename);
-            return true;
-          }
-        } catch (e) {
-          console.error(e);
-        }
-        return false;
-      }
-
-      var _rollbarConfig = {
+      let _rollbarConfig = {
        accessToken: 'POST_CLIENT_ITEM_TOKEN',
        rollbarJsUrl: '/dist/rollbar.js',
        captureUncaught: true,
-        //checkIgnore: ignoreFilesUncaught,
        payload: {
          environment: 'test',
        },
      };
-    </script>


This script wasn't being used.

matux · 2025-09-04T14:41:26Z

    <title>Webpack Example</title>

-    <script src="../dist/bundle.js"></script>
+    <script src="/examples/webpack/dist/bundle.js"></script>


WTR/Playwright quirk, uses project root not current dir

matux · 2025-09-04T14:42:40Z

-    // Karma headless chrome won't dispatch DOMContentLoaded,
-    // so we need to do it manually.
-    var event = document.createEvent('Event');
-    event.initEvent('DOMContentLoaded', true, true);
-    document.dispatchEvent(event);
+    // DOMContentLoaded is not dispatched automatically in WTR/Playwright
+    document.dispatchEvent(new Event('DOMContentLoaded', { bubbles: true }));


event.initEvent is deprecated.

matux · 2025-09-04T14:43:41Z

-    setTimeout(function () {
-      done();
-    }, 1000);
+    await setTimeout(250);


1s wait is unnecessary and slows the test down, 10 is enough, left 250 just in case.

matux · 2025-09-04T14:44:54Z

+    // Prevent WTR/Mocha from failing the test on uncaught errors.
+    __originalOnError = window.onerror;
+    window.onerror = () => false;


We store the original error and replace it with one that just returns false to signal the exception has been handled and to prevent propagation. Then Rollbar will swap its onerror with this one instead of WTR/Mocha/React's.

matux · 2025-09-04T14:45:26Z

-    document.write(window.__html__['examples/universal-browser/test.html']);
+    await loadHtml('examples/universal-browser/test.html');


write is deprecated. window.__html__ is Karma magic, so we needed a new way to load HTML.

matux · 2025-09-04T14:47:39Z

 # 1. there being minified snippets all over the place and
 # 2. some tests fail cause they depend on some sources being exactly as they are
 examples
+!test/examples


prettify was ignoring js files in test/examples.

brianr

LGTM.

* Initial Karma to Web Test Runner migration (#1289) * Fix hanging tests and expand WTR migration (#1295) * Migrate example tests for Web Test Runner (#1298) * Migrate browser transform and core tests for Web Test Runner (#1299) * Migrate browser tests from Karma to Web Test Runner (#1300) * Initial migration of react native tests (#1301) * Remove Grunt and Karma (#1302)

Example tests migrated to play nice with WTR

67a266c

matux requested a review from Copilot September 4, 2025 14:26

matux self-assigned this Sep 4, 2025

Copilot AI reviewed Sep 4, 2025

matux commented Sep 4, 2025

View reviewed changes

brianr approved these changes Sep 4, 2025

View reviewed changes

Minor changes (chai 5 syntax)

f662756

matux merged commit c2de6ac into matux/wtr Sep 5, 2025
4 checks passed

matux deleted the matux/wtr-examples branch September 5, 2025 18:45

matux mentioned this pull request Sep 8, 2025

[Meta-branch] Karma -> WTR migration and Grunt removal #1303

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Migrate example tests for Web Test Runner#1298

Migrate example tests for Web Test Runner#1298
matux merged 2 commits into
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		document.write(window.__html__['examples/universal-browser/test.html']);
		await loadHtml('examples/universal-browser/test.html');

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Description of the change

New Test Utilities

Migrated Example Tests

Fixes

Test Results

Technical Notes

Related issues

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matux commented Sep 4, 2025 •

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