test_runner: support custom message for expectFailure

Update `expectFailure` option to accept a string message and
display it in the TAP reporter output.

Example output: `# EXPECTED FAILURE <reason>`

Author: Han5991

doc/api/test.md

@@ -245,6 +245,10 @@ it.expectFailure('should do the thing', () => {
 it('should do the thing', { expectFailure: true }, () => {
   assert.strictEqual(doTheThing(), true);
 });
+
+it('should do the thing', { expectFailure: 'flaky test' }, () => {
+  assert.strictEqual(doTheThing(), true);
+});
 ```
 
 `skip` and/or `todo` are mutually exclusive to `expectFailure`, and `skip` or `todo`
@@ -1683,6 +1687,9 @@ changes:
     thread. If `false`, only one test runs at a time.
     If unspecified, subtests inherit this value from their parent.
     **Default:** `false`.
+  * `expectFailure` {boolean|string} If truthy, the test is expected to fail.
+    If a string is provided, that string is displayed in the test results as the
+    reason why the test is expected to fail. **Default:** `false`.
   * `only` {boolean} If truthy, and the test context is configured to run
     `only` tests, then this test will be run. Otherwise, the test is skipped.
     **Default:** `false`.

lib/internal/test_runner/reporter/tap.js

@@ -77,7 +77,7 @@ function reportTest(nesting, testNumber, status, name, skip, todo, expectFailure
   } else if (todo !== undefined) {
     line += ` # TODO${typeof todo === 'string' && todo.length ? ` ${tapEscape(todo)}` : ''}`;
   } else if (expectFailure !== undefined) {
-    line += ' # EXPECTED FAILURE';
+    line += ` # EXPECTED FAILURE${typeof expectFailure === 'string' && expectFailure.length ? ` ${tapEscape(expectFailure)}` : ''}`;
   }
 
   line += '\n';

lib/internal/test_runner/test.js

@@ -636,7 +636,13 @@ class Test extends AsyncResource {
     this.plan = null;
     this.expectedAssertions = plan;
     this.cancelled = false;
-    this.expectFailure = expectFailure !== undefined && expectFailure !== false;
+    if (expectFailure === undefined || expectFailure === false) {
+      this.expectFailure = false;
+    } else if (typeof expectFailure === 'string') {
+      this.expectFailure = expectFailure;
+    } else {
+      this.expectFailure = true;
+    }
     this.skipped = skip !== undefined && skip !== false;
     this.isTodo = (todo !== undefined && todo !== false) || this.parent?.isTodo;
     this.startTime = null;
@@ -948,11 +954,7 @@ class Test extends AsyncResource {
       return;
     }
 
-    if (this.expectFailure === true) {
-      this.passed = true;
-    } else {
-      this.passed = false;
-    }
+    this.passed = this.expectFailure;
 
     this.error = err;
   }
@@ -1359,7 +1361,7 @@ class Test extends AsyncResource {
     } else if (this.isTodo) {
       directive = this.reporter.getTodo(this.message);
     } else if (this.expectFailure) {
-      directive = this.reporter.getXFail(this.expectFailure); // TODO(@JakobJingleheimer): support specifying failure
+      directive = this.reporter.getXFail(this.expectFailure);
     }
 
     if (this.reportedType) {

test/parallel/test-runner-xfail-message.js

@@ -0,0 +1,25 @@
+'use strict';
+const common = require('../common');
+const { test } = require('node:test');
+const { spawn } = require('child_process');
+const assert = require('node:assert');
+
+if (process.env.CHILD_PROCESS === 'true') {
+  test('fail with message', { expectFailure: 'flaky test reason' }, () => {
+    assert.fail('boom');
+  });
+} else {
+  const child = spawn(process.execPath, ['--test-reporter', 'tap', __filename], {
+    env: { ...process.env, CHILD_PROCESS: 'true' },
+    stdio: 'pipe',
+  });
+
+  let stdout = '';
+  child.stdout.setEncoding('utf8');
+  child.stdout.on('data', (chunk) => { stdout += chunk; });
+
+  child.on('close', common.mustCall((code) => {
+    assert.strictEqual(code, 0);
+    assert.match(stdout, /# EXPECTED FAILURE flaky test reason/);
+  }));
+}