diff --git a/polygerrit-ui/app/api/diff.ts b/polygerrit-ui/app/api/diff.ts
index ad83fb8..724141f 100644
--- a/polygerrit-ui/app/api/diff.ts
+++ b/polygerrit-ui/app/api/diff.ts
@@ -406,17 +406,26 @@
   ): void;
 }
 
-// The current setup requires API users to register GrDiff instances with the
-// cursor, but we do not at this point want to expose the API that GrDiffCursor
-// uses to the public as it is likely to change. So for now, we allow any type
-// and cast. This works fine so long as API users do provide whatever the
-// gr-diff tag creates.
-export type GrDiff = unknown;
+/** An instance of the GrDiff Webcomponent */
+export interface GrDiff extends HTMLElement {
+  /**
+   * Return line number element for reading only,
+   *
+   * This is useful e.g. to determine where on screen certain lines are,
+   * whether they are covered up etc.
+   */
+  getLineNumEls(side: Side): readonly HTMLElement[];
+}
 
 /** A service to interact with the line cursor in gr-diff instances. */
 export declare interface GrDiffCursor {
-  replaceDiffs(diffs: GrDiff[]): void;
-  unregisterDiff(diff: GrDiff): void;
+  // The current setup requires API users to register GrDiff instances with the
+  // cursor, but we do not at this point want to expose the API that GrDiffCursor
+  // uses to the public as it is likely to change. So for now, we allow any type
+  // and cast. This works fine so long as API users do provide whatever the
+  // gr-diff tag creates.
+  replaceDiffs(diffs: unknown[]): void;
+  unregisterDiff(diff: unknown): void;
 
   isAtStart(): boolean;
   isAtEnd(): boolean;
diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.ts b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.ts
index ab8e404..516a31e 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.ts
@@ -939,7 +939,7 @@
   });
 
   suite('plugin endpoints', () => {
-    test('endpoint params', done => {
+    test('endpoint params', async () => {
       element.change = createParsedChange();
       element.revision = createRevision();
       interface MetadataGrEndpointDecorator extends GrEndpointDecorator {
@@ -961,12 +961,10 @@
         'http://some/plugins/url.js'
       );
       getPluginLoader().loadPlugins([]);
-      flush(() => {
-        assert.strictEqual(hookEl!.plugin, plugin);
-        assert.strictEqual(hookEl!.change, element.change);
-        assert.strictEqual(hookEl!.revision, element.revision);
-        done();
-      });
+      await flush();
+      assert.strictEqual(hookEl!.plugin, plugin!);
+      assert.strictEqual(hookEl!.change, element.change);
+      assert.strictEqual(hookEl!.revision, element.revision);
     });
   });
 });
diff --git a/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog_test.ts b/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog_test.ts
index 52ec8af..ea3c01d 100644
--- a/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog_test.ts
@@ -31,6 +31,7 @@
   RepoName,
 } from '../../../types/common';
 import {GrDownloadDialog} from './gr-download-dialog';
+import {mockPromise} from '../../../test/test-utils';
 
 const basicFixture = fixtureFromElement('gr-download-dialog');
 
@@ -168,14 +169,16 @@
       );
     });
 
-    test('close event', done => {
+    test('close event', async () => {
+      const closeCalled = mockPromise();
       element.addEventListener('close', () => {
-        done();
+        closeCalled.resolve();
       });
       const closeButton = element.shadowRoot!.querySelector(
         '.closeButtonContainer gr-button'
       );
       tap(closeButton!);
+      await closeCalled;
     });
   });
 
diff --git a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_test.ts b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_test.ts
index ae9af4a..15bc6bf 100644
--- a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_test.ts
@@ -599,7 +599,7 @@
       resetPlugins();
     });
 
-    test('endpoint params', done => {
+    test('endpoint params', async () => {
       element.change = {...createParsedChange(), labels: {}};
       interface RelatedChangesListGrEndpointDecorator
         extends GrEndpointDecorator {
@@ -620,11 +620,9 @@
         'http://some/plugins/url1.js'
       );
       getPluginLoader().loadPlugins([]);
-      flush(() => {
-        assert.strictEqual(hookEl.plugin, plugin);
-        assert.strictEqual(hookEl.change, element.change);
-        done();
-      });
+      await flush();
+      assert.strictEqual(hookEl!.plugin, plugin!);
+      assert.strictEqual(hookEl!.change, element.change);
     });
   });
 });
diff --git a/polygerrit-ui/app/elements/change/gr-reviewer-list/gr-reviewer-list_test.ts b/polygerrit-ui/app/elements/change/gr-reviewer-list/gr-reviewer-list_test.ts
index 4b57651..354d360 100644
--- a/polygerrit-ui/app/elements/change/gr-reviewer-list/gr-reviewer-list_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-reviewer-list/gr-reviewer-list_test.ts
@@ -17,7 +17,11 @@
 
 import '../../../test/common-test-setup-karma';
 import './gr-reviewer-list';
-import {queryAndAssert, stubRestApi} from '../../../test/test-utils';
+import {
+  mockPromise,
+  queryAndAssert,
+  stubRestApi,
+} from '../../../test/test-utils';
 import {GrReviewerList} from './gr-reviewer-list';
 import {
   createAccountDetailWithId,
@@ -53,12 +57,14 @@
     );
   });
 
-  test('add reviewer button opens reply dialog', done => {
+  test('add reviewer button opens reply dialog', async () => {
+    const dialogShown = mockPromise();
     element.addEventListener('show-reply-dialog', () => {
-      done();
+      dialogShown.resolve();
     });
-    flush();
+    await flush();
     tap(queryAndAssert(element, '.addReviewer'));
+    await dialogShown;
   });
 
   test('only show remove for removable reviewers', () => {
diff --git a/polygerrit-ui/app/elements/core/gr-error-dialog/gr-error-dialog_test.ts b/polygerrit-ui/app/elements/core/gr-error-dialog/gr-error-dialog_test.ts
index fa57a23..2dec8d2 100644
--- a/polygerrit-ui/app/elements/core/gr-error-dialog/gr-error-dialog_test.ts
+++ b/polygerrit-ui/app/elements/core/gr-error-dialog/gr-error-dialog_test.ts
@@ -17,7 +17,7 @@
 
 import * as MockInteractions from '@polymer/iron-test-helpers/mock-interactions';
 import '../../../test/common-test-setup-karma';
-import {queryAndAssert} from '../../../test/test-utils';
+import {mockPromise, queryAndAssert} from '../../../test/test-utils';
 import {GrDialog} from '../../shared/gr-dialog/gr-dialog';
 import {GrErrorDialog} from './gr-error-dialog';
 
@@ -30,10 +30,12 @@
     element = basicFixture.instantiate();
   });
 
-  test('dismiss tap fires event', done => {
-    element.addEventListener('dismiss', () => done());
+  test('dismiss tap fires event', async () => {
+    const dismissCalled = mockPromise();
+    element.addEventListener('dismiss', () => dismissCalled.resolve());
     MockInteractions.tap(
       (queryAndAssert(element, '#dialog') as GrDialog).$.confirm
     );
+    await dismissCalled;
   });
 });
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
index 7c437fd..0b42f9f 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
@@ -69,6 +69,7 @@
 import {
   CreateCommentEventDetail as CreateCommentEventDetailApi,
   RenderPreferences,
+  GrDiff as GrDiffApi,
 } from '../../../api/diff';
 import {isSafari, toggleClass} from '../../../utils/dom-util';
 import {assertIsDefined} from '../../../utils/common-util';
@@ -109,7 +110,7 @@
 }
 
 @customElement('gr-diff')
-export class GrDiff extends PolymerElement {
+export class GrDiff extends PolymerElement implements GrDiffApi {
   static get template() {
     return htmlTemplate;
   }
@@ -322,6 +323,12 @@
     super.disconnectedCallback();
   }
 
+  getLineNumEls(side: Side): HTMLElement[] {
+    return Array.from(
+      this.root?.querySelectorAll<HTMLElement>(`.lineNum.${side}`) ?? []
+    );
+  }
+
   showNoChangeMessage(
     loading?: boolean,
     prefs?: DiffPreferencesInfo,
diff --git a/polygerrit-ui/app/elements/settings/gr-agreements-list/gr-agreements-list_test.ts b/polygerrit-ui/app/elements/settings/gr-agreements-list/gr-agreements-list_test.ts
index f08976f..4891759 100644
--- a/polygerrit-ui/app/elements/settings/gr-agreements-list/gr-agreements-list_test.ts
+++ b/polygerrit-ui/app/elements/settings/gr-agreements-list/gr-agreements-list_test.ts
@@ -25,7 +25,7 @@
 suite('gr-agreements-list tests', () => {
   let element: GrAgreementsList;
 
-  setup(done => {
+  setup(async () => {
     const agreements: ContributorAgreementInfo[] = [
       {
         url: 'some url',
@@ -38,9 +38,8 @@
 
     element = basicFixture.instantiate();
 
-    element.loadData().then(() => {
-      flush(done);
-    });
+    await element.loadData();
+    await flush();
   });
 
   test('renders', () => {
diff --git a/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_test.ts b/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_test.ts
index 9f54cd1..d634483 100644
--- a/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_test.ts
+++ b/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_test.ts
@@ -125,16 +125,15 @@
     },
   ];
 
-  setup(done => {
+  setup(async () => {
     stubRestApi('getConfig').returns(Promise.resolve(config));
     stubRestApi('getAccountGroups').returns(Promise.resolve(groups));
     stubRestApi('getAccountAgreements').returns(
       Promise.resolve(signedAgreements)
     );
     element = basicFixture.instantiate();
-    element.loadData().then(() => {
-      flush(done);
-    });
+    await element.loadData();
+    await flush();
   });
 
   test('renders as expected with signed agreement', () => {