--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -624659,17 +624659,17 @@
    "32cd3419ff904a2440d9a6eaa7cb28f78d4a7e32",
    "testharness"
   ],
   "workers/modules/dedicated-worker-import.html": [
    "0b839e87ae98ad1abf32216a2086334cbc011ac0",
    "testharness"
   ],
   "workers/modules/dedicated-worker-options-credentials.html": [
-   "1d6a1629f81d26efcd05bf1c7d40011609238f4f",
+   "f182ac364e933ce744b18c0ca6e03ae975a883a3",
    "testharness"
   ],
   "workers/modules/dedicated-worker-options-credentials.html.headers": [
    "0de4f6326452e016161eabf248e047253507b79d",
    "support"
   ],
   "workers/modules/dedicated-worker-options-type.html": [
    "9f6f1be759beb885e2baa746e36ace83685f649b",

--- a/testing/web-platform/tests/workers/modules/dedicated-worker-options-credentials.html
+++ b/testing/web-platform/tests/workers/modules/dedicated-worker-options-credentials.html
@@ -12,67 +12,74 @@
 function DetermineExpectedCookieValue(options) {
   // Classic script loading should always send credentials regardless of the
   // 'credentials' option because the spec says the option takes effect only
   // for module script loading.
   if (options.type == 'classic')
     return 'COOKIE_VALUE';
   assert_equals(options.type, 'module');
 
-  if (!options.credentials || options.credentials == 'omit')
+  if (!options.credentials ||
+      options.credentials == 'same-origin' ||
+      options.credentials == 'include') {
+    return 'COOKIE_VALUE';
+  }
+  if (options.credentials == 'omit')
     return '';
-  if (options.credentials == 'same-origin' || options.credentials == 'include')
-    return 'COOKIE_VALUE';
   assert_unreached('Invalid credentials option was specified: ' +
                    options.credentials);
 }
 
 // Runs a credentials test with the given WorkerOptions.
-async function runCredentialsTest(options) {
-  const worker = new Worker('resources/credentials.py', options);
+function credentials_test(options, description) {
+  promise_test(async () => {
+    const worker = new Worker('resources/credentials.py', options);
 
-  // Wait until the worker sends the actual cookie value.
-  const msg_event = await new Promise(resolve => worker.onmessage = resolve);
+    // Wait until the worker sends the actual cookie value.
+    const msg_event = await new Promise(resolve => worker.onmessage = resolve);
 
-  const expectedCookieValue = DetermineExpectedCookieValue(options);
-  assert_equals(msg_event.data, expectedCookieValue);
+    const expectedCookieValue = DetermineExpectedCookieValue(options);
+    assert_equals(msg_event.data, expectedCookieValue);
+  }, description);
 }
 
 // Tests for module scripts.
 
-promise_test(() => runCredentialsTest({ type: 'module'}),
-    'new Worker() with the default credentials option should not send ' +
-    'the credentials');
+credentials_test(
+    { type: 'module'},
+    'new Worker() with the default credentials option should behave as ' +
+    'credentials=same-origin and send the credentials');
 
-promise_test(() => runCredentialsTest({ credentials: 'omit',
-                                        type: 'module' }),
+credentials_test(
+    { credentials: 'omit', type: 'module' },
     'new Worker() with credentials=omit should not send the credentials');
 
-promise_test(() => runCredentialsTest({ credentials: 'same-origin',
-                                        type: 'module' }),
+credentials_test(
+    { credentials: 'same-origin', type: 'module' },
     'new Worker() with credentials=same-origin should send the credentials');
 
-promise_test(() => runCredentialsTest({ credentials: 'include',
-                                        type: 'module' }),
+credentials_test(
+    { credentials: 'include', type: 'module' },
     'new Worker() with credentials=include should send the credentials');
 
 // Tests for classic scripts.
 
-promise_test(() => runCredentialsTest({ type: 'classic' }),
+credentials_test(
+    { type: 'classic' },
     'new Worker() with type=classic should always send the credentials ' +
     'regardless of the credentials option (default).');
 
-promise_test(() => runCredentialsTest({ credentials: 'omit',
-                                        type: 'classic' }),
+credentials_test(
+    { credentials: 'omit', type: 'classic' },
     'new Worker() with type=classic should always send the credentials ' +
     'regardless of the credentials option (omit).');
 
-promise_test(() => runCredentialsTest({ credentials: 'same-origin',
-                                        type: 'classic' }),
+credentials_test(
+    { credentials: 'same-origin', type: 'classic' },
     'new Worker() with type=classic should always send the credentials ' +
     'regardless of the credentials option (same-origin).');
 
-promise_test(() => runCredentialsTest({ credentials: 'include',
-                                        type: 'classic' }),
+credentials_test(
+    { credentials: 'include', type: 'classic' },
     'new Worker() with type=classic should always send the credentials ' +
     'regardless of the credentials option (include).');
 
 </script>