Update test name on tests-start, guard against double-prefixing

When only the test-result event renames tests, live progress reporting
(the tests-start event) still shows the unprefixed name, so a running
test cannot be attributed to its partition/browser. Renaming on
tests-start as well fixes that, and updateTestName now returns early
if the name already carries the prefix so the two hooks do not stack
prefixes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: NullVoxPopuli

addon-test-support/-private/patch-testem-output.js

@@ -9,6 +9,11 @@
  * @return {string} testName
  */
 export function updateTestName(urlParams, testName) {
+  if (testName.includes('Exam Partition') || testName.includes('Browser Id')) {
+    // The test name was already updated, e.g. by the `tests-start` event
+    return testName;
+  }
+
   const split = urlParams.get('split');
   const loadBalance = urlParams.get('loadBalance');
 
@@ -31,12 +36,18 @@ export function updateTestName(urlParams, testName) {
 }
 
 /**
- * Setup testem test-result event to update the test name when a test completes
+ * Setup testem tests-start and test-result events to update the test name
+ * when a test starts and when it completes
  *
  * @function patchTestemOutput
  * @param {Map} urlParams
  */
 export function patchTestemOutput(urlParams) {
+  Testem.on('tests-start', (test) => {
+    if (test?.name) {
+      test.name = updateTestName(urlParams, test.name);
+    }
+  });
   Testem.on('test-result', (test) => {
     test.name = updateTestName(urlParams, test.name);
   });

tests/unit/testem-output-test.js

@@ -99,5 +99,63 @@ module('Unit | patch-testem-output', function () {
         'Exam Partition 2 - Browser Id 1 - test_module | test_name',
       );
     });
+
+    test('does not add partition number again when the test name already contains it', function (assert) {
+      assert.deepEqual(
+        TestemOutput.updateTestName(
+          new Map().set('split', 2).set('partition', 2),
+          'Exam Partition 2 - test_module | test_name',
+        ),
+        'Exam Partition 2 - test_module | test_name',
+      );
+    });
+
+    test('does not add browser number again when the test name already contains it', function (assert) {
+      assert.deepEqual(
+        TestemOutput.updateTestName(
+          new Map().set('loadBalance', 2).set('browser', 1),
+          'Browser Id 1 - test_module | test_name',
+        ),
+        'Browser Id 1 - test_module | test_name',
+      );
+    });
+  });
+
+  module('patchTestemOutput', function (hooks) {
+    let originalTestem;
+    let handlers;
+
+    hooks.beforeEach(function () {
+      originalTestem = window.Testem;
+      handlers = new Map();
+      window.Testem = {
+        on(event, callback) {
+          handlers.set(event, callback);
+        },
+      };
+    });
+
+    hooks.afterEach(function () {
+      window.Testem = originalTestem;
+    });
+
+    test('updates the test name when a test starts and when it completes', function (assert) {
+      TestemOutput.patchTestemOutput(new Map().set('split', 2));
+
+      const test = { name: 'test_module | test_name' };
+      handlers.get('tests-start')(test);
+      assert.deepEqual(test.name, 'Exam Partition 1 - test_module | test_name');
+
+      handlers.get('test-result')(test);
+      assert.deepEqual(test.name, 'Exam Partition 1 - test_module | test_name');
+    });
+
+    test('handles tests-start events without a test name', function (assert) {
+      TestemOutput.patchTestemOutput(new Map().set('split', 2));
+
+      const test = {};
+      handlers.get('tests-start')(test);
+      assert.deepEqual(test.name, undefined);
+    });
   });
 });