I need to modify the repository and inspect it further. The user mentioned that the rel=noopener audit should ignore mailto links, which seems to be related to a request issue. I should identify the specific project involved. First, I'll start with a preamble to explain what I'm doing and then proceed with the relevant commands. This way, the user will know I'm addressing their concerns directly!

I’ll locate the noopener audit and its tests, then make mailto: links exempt.

pwd && rg -n "noopener|rel.*audit|target=.*_blank" . --glob '!node_modules' --glob '!vendor'

Chunk ID: 159d7e
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2232
Output:
/testbed
./lighthouse-cli/test/smokehouse/dobetterweb/dbw-expectations.js:50:      'external-anchors-use-rel-noopener': {
./lighthouse-cli/test/smokehouse/dobetterweb/dbw-expectations.js:301:      'external-anchors-use-rel-noopener': {
./docs/understanding-results.md:187:| result | `Object` | The actual audit result, a copy of the audit object found in [audits](#audits). *NOTE: this property will likely be removed in upcoming releases; use the `id` property to lookup the result in the `audits` property.* |
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:22:<!-- we use a relative protocol url to test that `new URL(resource)` in the critical-request-chains.js audit can handle it -->
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:103:<template id="noopener-links-tmpl">
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:104:  <!-- FAIL - does not use rel="noopener" to open external link -->
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:105:  <a href="https://www.google.com/" target="_blank">external link</a>
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:106:  <!-- FAIL - does not use rel="noopener" and has no href attribute, giving an
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:108:  <a target="_blank">external link</a>
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:110:  <a href="https://www.google.com/" target="_blank" rel="noopener nofollow">external link that uses rel noopener and another unrelated rel attribute</a>
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:112:  <a href="./doesnotexist" target="_blank">internal link is ok</a>
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:294:  stampTemplate('noopener-links-tmpl', document.body);
./lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html:374:  if (params.has('relnoopener')) {
./changelog.md:24:* audit: Ignore `href=javascript:.*` for `rel=noopener` audit ([#3574](https://github.com/googlechrome/lighthouse/pull/3574))
./changelog.md:298:Thanks to Katie Hempenius, Artur M, Kevin Farrugia, Piper Chester, Robin Drexler, and Mike Deverell. Due to the effort of these developers we now have an audit for checking for paste-blocked password fields, unified usage of toLocaleString(), a correct gulp recipe, a well-functioning chrome-launcher module, and improved clarity in the audit test descriptions.  **We truly appreciate all these improvements!**
./changelog.md:882:- **Audit:** Handle invalid URLs in `external-anchors-use-rel-noopener` audit - #1358
./changelog.md:927:- **Audit:** handle anchor tags with no href in 'external-anchors-use-rel-noopener' audit - #1238
./changelog.md:1030:- **Audit:** identify `noopener` when in list of link types in `rel` - #1035
./changelog.md:1089:- **Audit:** Add DBW audit for `rel=noopener` on external links - #912
./lighthouse-core/test/results/sample_v2.json:1198:      "helpText": "When a button doesn't have an accessible name, screen readers announce it as \"button\", making it unusable for users who rely on screen readers. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/button-name)."
./lighthouse-core/test/results/sample_v2.json:1533:      "helpText": "A value greater than 0 implies an explicit navigation ordering. Although technically valid, this often creates frustrating experiences for users who rely on assistive technologies. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/tabindex)."
./lighthouse-core/test/results/sample_v2.json:2135:    "external-anchors-use-rel-noopener": {
./lighthouse-core/test/results/sample_v2.json:2146:            "url": "<a href=\"https://www.google.com/\" target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:2152:            "url": "<a target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:2158:            "url": "<a href=\"./doesnotexist\" target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:2163:      "name": "external-anchors-use-rel-noopener",
./lighthouse-core/test/results/sample_v2.json:2165:      "description": "Opens external anchors using `rel=\"noopener\"`",
./lighthouse-core/test/results/sample_v2.json:2166:      "helpText": "Open new tabs using `rel=\"noopener\"` to improve performance and prevent security vulnerabilities. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/noopener).",
./lighthouse-core/test/results/sample_v2.json:5125:            "helpText": "When a button doesn't have an accessible name, screen readers announce it as \"button\", making it unusable for users who rely on screen readers. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/button-name)."
./lighthouse-core/test/results/sample_v2.json:5580:            "helpText": "A value greater than 0 implies an explicit navigation ordering. Although technically valid, this often creates frustrating experiences for users who rely on assistive technologies. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/tabindex)."
./lighthouse-core/test/results/sample_v2.json:6392:          "id": "external-anchors-use-rel-noopener",
./lighthouse-core/test/results/sample_v2.json:6405:                  "url": "<a href=\"https://www.google.com/\" target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:6411:                  "url": "<a target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:6417:                  "url": "<a href=\"./doesnotexist\" target=\"_blank\">"
./lighthouse-core/test/results/sample_v2.json:6422:            "name": "external-anchors-use-rel-noopener",
./lighthouse-core/test/results/sample_v2.json:6424:            "description": "Opens external anchors using `rel=\"noopener\"`",
./lighthouse-core/test/results/sample_v2.json:6425:            "helpText": "Open new tabs using `rel=\"noopener\"` to improve performance and prevent security vulnerabilities. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/noopener).",
./lighthouse-core/test/report/v2/renderer/dom-test.js:82:          'Some <a rel="noopener" target="_blank" href="https://example.com/foo">link</a>. ' +
./lighthouse-core/test/report/v2/renderer/dom-test.js:83:          '<a rel="noopener" target="_blank" href="http://example.com/">Learn more</a>.');
./lighthouse-core/test/report/v2/renderer/dom-test.js:87:          '<a rel="noopener" target="_blank" href="https://example.com/foo">link</a>',
./lighthouse-core/test/report/v2/renderer/dom-test.js:93:          '<a rel="noopener" target="_blank" href="https://example.com/foo"> Link </a> ' +
./lighthouse-core/test/report/v2/renderer/dom-test.js:115:          'good. <a rel="noopener" target="_blank" href="https://dequeuniversity.com/rules/axe/2.2/td-headers-attr">Learn more</a>.');
./lighthouse-core/test/report/v2/renderer/details-renderer-test.js:199:      assert.equal(el.rel, 'noopener');
./lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js:9:  require('../../../audits/dobetterweb/external-anchors-use-rel-noopener.js');
./lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js:16:describe('External anchors use rel="noopener"', () => {
./lighthouse-core/report/v2/templates.html:324:      <div class="lh-metadata__results">Results for: <a href="" class="lh-metadata__url" target="_blank" rel="noopener"><!-- fill me --></a></div>
./lighthouse-core/report/v2/templates.html:386:      <a href="https://github.com/GoogleChrome/Lighthouse/issues" target="_blank" rel="noopener">File an issue</a>
./lighthouse-core/report/v2/renderer/dom.js:108:        a.rel = 'noopener';
./lighthouse-core/report/v2/renderer/details-renderer.js:107:    a.rel = 'noopener';
./lighthouse-core/gather/gatherers/dobetterweb/anchors-with-no-rel-noopener.js:19:      const selector = 'a[target="_blank"]:not([rel~="noopener"])';
./lighthouse-core/config/default.js:30:      'dobetterweb/anchors-with-no-rel-noopener',
./lighthouse-core/config/default.js:153:    'dobetterweb/external-anchors-use-rel-noopener',
./lighthouse-core/config/default.js:340:        {id: 'external-anchors-use-rel-noopener', weight: 1},
./lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:17:      name: 'external-anchors-use-rel-noopener',
./lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:18:      description: 'Opens external anchors using `rel="noopener"`',
./lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:19:      failureDescription: 'Does not open external anchors using `rel="noopener"`',
./lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:20:      helpText: 'Open new tabs using `rel="noopener"` to improve performance and ' +
./lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:22:          '[Learn more](https://developers.google.com/web/tools/lighthouse/audits/noopener).',

I need to take a closer look at the instructions and the files available. I'm thinking maybe there are root AGENTS present in the current working directory, but I’m not sure. The developer mentioned that the root AGENT is included, but I can’t seem to find anything. So, I guess I’ll need to use ls or find to search for any applicable files or indications related to the AGENTS. Let's see what I can uncover!

rg --files -g 'AGENTS.md' -g '!node_modules' -g '!vendor' /testbed / 2>/dev/null | head -80

Chunk ID: 065d07
Wall time: 0.0480 seconds
Process exited with code 0
Original token count: 0
Output:

sed -n '1,240p' lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js && printf '\n--- TEST ---\n' && sed -n '1,280p' lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js

Chunk ID: 338291
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1478
Output:
/**
 * @license Copyright 2016 Google Inc. All Rights Reserved.
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
 */
'use strict';
​
const URL = require('../../lib/url-shim');
const Audit = require('../audit');
​
class ExternalAnchorsUseRelNoopenerAudit extends Audit {
  /**
   * @return {!AuditMeta}
   */
  static get meta() {
    return {
      name: 'external-anchors-use-rel-noopener',
      description: 'Opens external anchors using `rel="noopener"`',
      failureDescription: 'Does not open external anchors using `rel="noopener"`',
      helpText: 'Open new tabs using `rel="noopener"` to improve performance and ' +
          'prevent security vulnerabilities. ' +
          '[Learn more](https://developers.google.com/web/tools/lighthouse/audits/noopener).',
      requiredArtifacts: ['URL', 'AnchorsWithNoRelNoopener'],
    };
  }
​
  /**
   * @param {!Artifacts} artifacts
   * @return {!AuditResult}
   */
  static audit(artifacts) {
    let debugString;
    const pageHost = new URL(artifacts.URL.finalUrl).host;
    // Filter usages to exclude anchors that are same origin
    // TODO: better extendedInfo for anchors with no href attribute:
    // https://github.com/GoogleChrome/lighthouse/issues/1233
    // https://github.com/GoogleChrome/lighthouse/issues/1345
    const failingAnchors = artifacts.AnchorsWithNoRelNoopener
      .filter(anchor => {
        try {
          return new URL(anchor.href).host !== pageHost;
        } catch (err) {
          debugString = 'Lighthouse was unable to determine the destination ' +
              'of some anchor tags. If they are not used as hyperlinks, ' +
              'consider removing the _blank target.';
          return true;
        }
      })
      .filter(anchor => {
        // Ignore href's that are not real links
        return !anchor.href || !anchor.href.toLowerCase().startsWith('javascript:');
      })
      .map(anchor => {
        return {
          href: anchor.href || 'Unknown',
          target: anchor.target || '',
          rel: anchor.rel || '',
          url: '<a' +
              (anchor.href ? ` href="${anchor.href}"` : '') +
              (anchor.target ? ` target="${anchor.target}"` : '') +
              (anchor.rel ? ` rel="${anchor.rel}"` : '') + '>',
        };
      });
​
    const headings = [
      {key: 'href', itemType: 'url', text: 'URL'},
      {key: 'target', itemType: 'text', text: 'Target'},
      {key: 'rel', itemType: 'text', text: 'Rel'},
    ];
​
    const details = Audit.makeTableDetails(headings, failingAnchors);
​
    return {
      rawValue: failingAnchors.length === 0,
      extendedInfo: {
        value: failingAnchors,
      },
      details,
      debugString,
    };
  }
}
​
module.exports = ExternalAnchorsUseRelNoopenerAudit;
​
--- TEST ---
/**
 * @license Copyright 2016 Google Inc. All Rights Reserved.
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
 */
'use strict';
​
const ExternalAnchorsAudit =
  require('../../../audits/dobetterweb/external-anchors-use-rel-noopener.js');
const assert = require('assert');
​
const URL = 'https://google.com/test';
​
/* eslint-env mocha */
​
describe('External anchors use rel="noopener"', () => {
  it('passes when links are from same hosts as the page host', () => {
    const auditResult = ExternalAnchorsAudit.audit({
      AnchorsWithNoRelNoopener: [
        {href: 'https://google.com/test'},
        {href: 'https://google.com/test1'},
      ],
      URL: {finalUrl: URL},
    });
    assert.equal(auditResult.rawValue, true);
    assert.equal(auditResult.details.items.length, 0);
    assert.equal(auditResult.details.items.length, 0);
  });
​
  it('fails when links are from different hosts than the page host', () => {
    const auditResult = ExternalAnchorsAudit.audit({
      AnchorsWithNoRelNoopener: [
        {href: 'https://example.com/test'},
        {href: 'https://example.com/test1'},
      ],
      URL: {finalUrl: URL},
    });
    assert.equal(auditResult.rawValue, false);
    assert.equal(auditResult.details.items.length, 2);
    assert.equal(auditResult.details.items.length, 2);
  });
​
  it('handles links with no href attribute', () => {
    const auditResult = ExternalAnchorsAudit.audit({
      AnchorsWithNoRelNoopener: [
        {href: ''},
        {href: 'http://'},
        {href: 'http:'},
      ],
      URL: {finalUrl: URL},
    });
    assert.equal(auditResult.rawValue, false);
    assert.equal(auditResult.details.items.length, 3);
    assert.equal(auditResult.details.items.length, 3);
    assert.ok(auditResult.debugString, 'includes debugString');
  });
​
  it('does not fail for links with javascript in href attribute', () => {
    const auditResult = ExternalAnchorsAudit.audit({
      AnchorsWithNoRelNoopener: [
        {href: 'javascript:void(0)'},
        {href: 'JAVASCRIPT:void(0)'},
      ],
      URL: {finalUrl: URL},
    });
    assert.equal(auditResult.rawValue, true);
    assert.equal(auditResult.details.items.length, 0);
  });
});

sed -n '90,125p' lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html && cat package.json | head -100 && git status --short

Chunk ID: 6b5fe4
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1393
Output:
  </style>
</template>
​
</head>
<body>
​
<div>
  <h2>Do better web tester page</h2>
  <span>Hi there!</span>
</div>
​
<section id="touchmove-section">touchmove section</section>
​
<template id="noopener-links-tmpl">
  <!-- FAIL - does not use rel="noopener" to open external link -->
  <a href="https://www.google.com/" target="_blank">external link</a>
  <!-- FAIL - does not use rel="noopener" and has no href attribute, giving an
    href value of '' when read, which will throw in a `new URL('')` constructor -->
  <a target="_blank">external link</a>
  <!-- PASS -->
  <a href="https://www.google.com/" target="_blank" rel="noopener nofollow">external link that uses rel noopener and another unrelated rel attribute</a>
  <!-- PASS -->
  <a href="./doesnotexist" target="_blank">internal link is ok</a>
</template>
​
<template id="password-inputs-can-be-pasted-into">
  <!-- FAIL - calls preventDefault on event -->
  <input type="password" onpaste="event.preventDefault();" />
  <!-- PASS -->
  <input type="password" />
  <!-- FAIL - returns false in event handler -->
  <input type="password" onpaste="return false;" />
​
</template>
​
<!-- FAIL(image-aspect-ratio): image is naturally 480x318 -->
{
  "name": "lighthouse",
  "version": "2.6.0",
  "description": "Lighthouse",
  "main": "./lighthouse-core/index.js",
  "bin": {
    "lighthouse": "./lighthouse-cli/index.js",
    "chrome-debug": "./chrome-launcher/manual-chrome-launcher.js"
  },
  "engines": {
    "node": ">=6"
  },
  "scripts": {
    "install-all": "npm-run-posix-or-windows install-all:task",
    "install-all:task": "yarn & yarn install-extension & yarn install-viewer & wait",
    "install-all:task:windows": "yarn && yarn install-extension && yarn install-viewer",
    "install-extension": "cd ./lighthouse-extension && yarn install",
    "install-viewer": "cd ./lighthouse-viewer && yarn install",
    "build-all": "npm-run-posix-or-windows build-all:task",
    "build-all:task": "yarn build-extension & yarn build-viewer & wait",
    "build-all:task:windows": "yarn build-extension && yarn build-viewer",
    "build-extension": "cd ./lighthouse-extension && yarn build",
    "build-viewer": "cd ./lighthouse-viewer && yarn build",
    "clean": "rimraf *.report.html *.report.dom.html *.report.json *.screenshots.html *.devtoolslog.json *.trace.json || true",
    "lint": "[ \"$CI\" = true ] && eslint --quiet -f codeframe . || eslint .",
    "smoke": "bash lighthouse-cli/test/smokehouse/run-all-tests.sh",
    "coverage": "istanbul cover -x \"**/third_party/**\" _mocha -- $(find */test -name '*-test.js') --timeout 10000 --reporter progress --report lcovonly",
    "coveralls": "yarn coverage && cat ./coverage/lcov.info | coveralls && ./node_modules/codecov/bin/codecov",
    "start": "node ./lighthouse-cli/index.js",
    "test": "yarn lint --quiet && yarn unit && yarn type-check && yarn closure",
    "unit-core": "bash lighthouse-core/scripts/run-mocha.sh --core",
    "unit-cli": "bash lighthouse-core/scripts/run-mocha.sh --cli",
    "unit-viewer": "bash lighthouse-core/scripts/run-mocha.sh --viewer",
    "unit": "bash lighthouse-core/scripts/run-mocha.sh --default",
    "core-unit": "yarn unit-core",
    "cli-unit": "yarn unit-cli",
    "viewer-unit": "yarn unit-viewer",
    "closure": "cd lighthouse-core && node closure/closure-type-checking.js",
    "devtools": "bash lighthouse-core/scripts/roll-to-devtools.sh",
    "compile-devtools": "bash lighthouse-core/scripts/compile-against-devtools.sh",
    "watch": "bash lighthouse-core/scripts/run-mocha.sh --watch",
    "chrome": "node chrome-launcher/manual-chrome-launcher.js",
    "fast": "yarn start -- --disable-device-emulation --disable-cpu-throttling --disable-network-throttling",
    "smokehouse": "node lighthouse-cli/test/smokehouse/smokehouse.js",
    "deploy-viewer": "cd lighthouse-viewer && gulp deploy",
    "bundlesize": "bundlesize",
    "plots-smoke": "bash plots/test/smoke.sh",
    "changelog": "conventional-changelog --config ./build/changelog-generator/index.js --infile changelog.md --same-file",
    "type-check": "tsc -p ."
  },
  "devDependencies": {
    "@types/configstore": "^2.1.1",
    "@types/inquirer": "^0.0.35",
    "@types/node": "*",
    "@types/opn": "^3.0.28",
    "@types/update-notifier": "^1.0.2",
    "@types/yargs": "^8.0.2",
    "babel-core": "^6.16.0",
    "bundlesize": "^0.14.4",
    "codecov": "^2.2.0",
    "commitizen": "^2.9.6",
    "conventional-changelog-cli": "^1.3.4",
    "coveralls": "^2.11.9",
    "cz-customizable": "^5.2.0",
    "eslint": "^4.8.0",
    "eslint-config-google": "^0.9.1",
    "google-closure-compiler": "^20170521.0.0",
    "gulp": "^3.9.1",
    "gulp-replace": "^0.5.4",
    "gulp-util": "^3.0.7",
    "istanbul": "^0.4.3",
    "jsdom": "^9.12.0",
    "mocha": "^3.2.0",
    "npm-run-posix-or-windows": "^2.0.2",
    "typescript": "^2.6.1",
    "zone.js": "^0.7.3"
  },
  "dependencies": {
    "axe-core": "2.4.1",
    "chrome-devtools-frontend": "1.0.422034",
    "chrome-launcher": "0.8.1",
    "configstore": "^3.1.1",
    "devtools-timeline-model": "1.1.6",
    "http-link-header": "^0.8.0",
    "inquirer": "^3.3.0",
    "jpeg-js": "0.1.2",
    "js-library-detector": "^4.0.0",
    "json-stringify-safe": "5.0.1",
    "lighthouse-logger": "^1.0.0",
    "metaviewport-parser": "0.1.0",
    "mkdirp": "0.5.1",
    "opn": "4.0.2",
    "parse-cache-control": "1.0.1",
    "raven": "^2.2.1",
    "rimraf": "^2.6.1",
    "semver": "^5.3.0",
    "speedline": "1.3.0",
    "update-notifier": "^2.1.0",
    "whatwg-url": "^6.3.0",
    "ws": "3.3.2",

I need to update the audit implementation to specifically exclude mailto links. The current filter ordering is causing issues since it's checking new URL mailto cases, and I need a way to parse this correctly. I should ensure JavaScript handling is included too. Maybe I can separate this with conditions to ignore actual links while still ensuring that mailto links aren't parsed incorrectly. Overall, I'm focused on simplifying the logic to avoid unnecessary URL parsing, while still being thorough in the audit checks.Updating Mailto Protocol Handling

It seems the new URL for mailto likely returns an empty host, which isn’t producing an exception. I should implement an extension in the predicate and set up a unit test that checks mixed-case mailto links, since that’s likely a requirement. There might be a need to create separate tests for mailto specifically. Also, I should consider adding a changelog entry for clarity and check if existing tests cover this. Focused changes are the goal, so I'll aim for simplicity while ensuring thorough testing.

The audit currently exempts javascript: only; I’ll add a case-insensitive mailto: exemption and regression test.

apply_patch <<'PATCH'
*** Begin Patch
*** Update File: lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
@@
       })
       .filter(anchor => {
-        // Ignore href's that are not real links
-        return !anchor.href || !anchor.href.toLowerCase().startsWith('javascript:');
+        // Ignore href's that are not real links or do not navigate to a page.
+        const href = (anchor.href || '').toLowerCase();
+        return !anchor.href || (!href.startsWith('javascript:') && !href.startsWith('mailto:'));
       })
*** Update File: lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js
@@
   it('does not fail for links with javascript in href attribute', () => {
     const auditResult = ExternalAnchorsAudit.audit({
       AnchorsWithNoRelNoopener: [
         {href: 'javascript:void(0)'},
@@
     assert.equal(auditResult.rawValue, true);
     assert.equal(auditResult.details.items.length, 0);
   });
+
+  it('does not fail for links with mailto in href attribute', () => {
+    const auditResult = ExternalAnchorsAudit.audit({
+      AnchorsWithNoRelNoopener: [
+        {href: 'mailto:sales@example.com'},
+        {href: 'MAILTO:support@example.com'},
+      ],
+      URL: {finalUrl: URL},
+    });
+    assert.equal(auditResult.rawValue, true);
+    assert.equal(auditResult.details.items.length, 0);
+  });
 });
*** End Patch
PATCH

Wall time: 0.0000 seconds
Output:
Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
M lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js

Patch is in; I’ll run the focused audit test and inspect the final diff.

./node_modules/.bin/mocha lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js --timeout 10000

Chunk ID: 648f78
Wall time: 0.2552 seconds
Process exited with code 0
Original token count: 92
Output:
​
​
  External anchors use rel="noopener"
    ✓ passes when links are from same hosts as the page host
    ✓ fails when links are from different hosts than the page host
    ✓ handles links with no href attribute
    ✓ does not fail for links with javascript in href attribute
    ✓ does not fail for links with mailto in href attribute
​
​
  5 passing (20ms)

git diff --check && git diff -- lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js && git status --short

Chunk ID: 59373a
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 510
Output:
diff --git a/lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js b/lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
index 296f94d..21b1147 100644
--- a/lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
+++ b/lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
@@ -47,8 +47,9 @@ class ExternalAnchorsUseRelNoopenerAudit extends Audit {
         }
       })
       .filter(anchor => {
-        // Ignore href's that are not real links
-        return !anchor.href || !anchor.href.toLowerCase().startsWith('javascript:');
+        // Ignore href's that are not real links or do not navigate to a page.
+        const href = (anchor.href || '').toLowerCase();
+        return !anchor.href || (!href.startsWith('javascript:') && !href.startsWith('mailto:'));
       })
       .map(anchor => {
         return {
diff --git a/lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js b/lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js
index c89aab4..ea8d777 100644
--- a/lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js
+++ b/lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js
@@ -66,4 +66,16 @@ describe('External anchors use rel="noopener"', () => {
     assert.equal(auditResult.rawValue, true);
     assert.equal(auditResult.details.items.length, 0);
   });
+
+  it('does not fail for links with mailto in href attribute', () => {
+    const auditResult = ExternalAnchorsAudit.audit({
+      AnchorsWithNoRelNoopener: [
+        {href: 'mailto:sales@example.com'},
+        {href: 'MAILTO:support@example.com'},
+      ],
+      URL: {finalUrl: URL},
+    });
+    assert.equal(auditResult.rawValue, true);
+    assert.equal(auditResult.details.items.length, 0);
+  });
 });
 M lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js
 M lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js

The unit test shows it can handle both lower and uppercase, and I have 5 validation tests passing, which is great! I don't see the need for any more tests at this point. However, I'm a bit concerned that the status output indicates only two modifications, but I'll keep an eye on that. Overall, it seems I can finalize with up to 10 lines.

Updated the rel="noopener" audit to ignore mailto: links, case-insensitively, in lighthouse-core/audits/dobetterweb/external-anchors-use-rel-noopener.js:50. Added lowercase and uppercase regression coverage in lighthouse-core/test/audits/dobetterweb/external-anchors-use-rel-noopener-test.js:69.

Validation: all 5 focused audit tests pass.