diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element_test.js b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element_test.js
index 196567e..44b0b8b 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element_test.js
@@ -751,7 +751,7 @@
     let outputEl;
     let keyLocations;
 
-    setup(done => {
+    setup(async () => {
       const prefs = {
         line_length: 10,
         show_tabs: true,
@@ -786,11 +786,11 @@
         return builder;
       });
       element.diff = {content};
-      element.render(keyLocations, prefs).then(done);
+      await element.render(keyLocations, prefs);
     });
 
-    test('addColumns is called', done => {
-      element.render(keyLocations, {}).then(done);
+    test('addColumns is called', async () => {
+      await element.render(keyLocations, {});
       assert.isTrue(element._builder.addColumns.called);
     });
 
@@ -812,15 +812,13 @@
       assert.strictEqual(sections[1], section[1]);
     });
 
-    test('render-start and render-content are fired', done => {
+    test('render-start and render-content are fired', async () => {
       const dispatchEventStub = sinon.stub(element, 'dispatchEvent');
-      element.render(keyLocations, {}).then(() => {
-        const firedEventTypes = dispatchEventStub.getCalls()
-            .map(c => c.args[0].type);
-        assert.include(firedEventTypes, 'render-start');
-        assert.include(firedEventTypes, 'render-content');
-        done();
-      });
+      await element.render(keyLocations, {});
+      const firedEventTypes = dispatchEventStub.getCalls()
+          .map(c => c.args[0].type);
+      assert.include(firedEventTypes, 'render-start');
+      assert.include(firedEventTypes, 'render-content');
     });
 
     test('cancel', () => {
@@ -837,7 +835,7 @@
     let prefs;
     let keyLocations;
 
-    setup(done => {
+    setup(async () => {
       element = mockDiffFixture.instantiate();
       diff = getMockDiffResponse();
       element.diff = diff;
@@ -849,10 +847,8 @@
       };
       keyLocations = {left: {}, right: {}};
 
-      element.render(keyLocations, prefs).then(() => {
-        builder = element._builder;
-        done();
-      });
+      await element.render(keyLocations, prefs);
+      builder = element._builder;
     });
 
     test('aria-labels on added line numbers', () => {
@@ -986,34 +982,30 @@
       assert.isTrue(lineNumberEl.classList.contains('right'));
     });
 
-    test('_getLineNumberEl unified left', done => {
+    test('_getLineNumberEl unified left', async () => {
       // Re-render as unified:
       element.viewMode = 'UNIFIED_DIFF';
-      element.render(keyLocations, prefs).then(() => {
-        builder = element._builder;
+      await element.render(keyLocations, prefs);
+      builder = element._builder;
 
-        const contentEl = builder.getContentByLine(5, 'left',
-            element.$.diffTable);
-        const lineNumberEl = builder._getLineNumberEl(contentEl, 'left');
-        assert.isTrue(lineNumberEl.classList.contains('lineNum'));
-        assert.isTrue(lineNumberEl.classList.contains('left'));
-        done();
-      });
+      const contentEl = builder.getContentByLine(5, 'left',
+          element.$.diffTable);
+      const lineNumberEl = builder._getLineNumberEl(contentEl, 'left');
+      assert.isTrue(lineNumberEl.classList.contains('lineNum'));
+      assert.isTrue(lineNumberEl.classList.contains('left'));
     });
 
-    test('_getLineNumberEl unified right', done => {
+    test('_getLineNumberEl unified right', async () => {
       // Re-render as unified:
       element.viewMode = 'UNIFIED_DIFF';
-      element.render(keyLocations, prefs).then(() => {
-        builder = element._builder;
+      await element.render(keyLocations, prefs);
+      builder = element._builder;
 
-        const contentEl = builder.getContentByLine(5, 'right',
-            element.$.diffTable);
-        const lineNumberEl = builder._getLineNumberEl(contentEl, 'right');
-        assert.isTrue(lineNumberEl.classList.contains('lineNum'));
-        assert.isTrue(lineNumberEl.classList.contains('right'));
-        done();
-      });
+      const contentEl = builder.getContentByLine(5, 'right',
+          element.$.diffTable);
+      const lineNumberEl = builder._getLineNumberEl(contentEl, 'right');
+      assert.isTrue(lineNumberEl.classList.contains('lineNum'));
+      assert.isTrue(lineNumberEl.classList.contains('right'));
     });
 
     test('_getNextContentOnSide side-by-side left', () => {
@@ -1040,44 +1032,38 @@
       assert.equal(nextElem.textContent, expectedNextString);
     });
 
-    test('_getNextContentOnSide unified left', done => {
+    test('_getNextContentOnSide unified left', async () => {
       // Re-render as unified:
       element.viewMode = 'UNIFIED_DIFF';
-      element.render(keyLocations, prefs).then(() => {
-        builder = element._builder;
+      await element.render(keyLocations, prefs);
+      builder = element._builder;
 
-        const startElem = builder.getContentByLine(5, 'left',
-            element.$.diffTable);
-        const expectedStartString = diff.content[2].ab[0];
-        const expectedNextString = diff.content[2].ab[1];
-        assert.equal(startElem.textContent, expectedStartString);
+      const startElem = builder.getContentByLine(5, 'left',
+          element.$.diffTable);
+      const expectedStartString = diff.content[2].ab[0];
+      const expectedNextString = diff.content[2].ab[1];
+      assert.equal(startElem.textContent, expectedStartString);
 
-        const nextElem = builder._getNextContentOnSide(startElem,
-            'left');
-        assert.equal(nextElem.textContent, expectedNextString);
-
-        done();
-      });
+      const nextElem = builder._getNextContentOnSide(startElem,
+          'left');
+      assert.equal(nextElem.textContent, expectedNextString);
     });
 
-    test('_getNextContentOnSide unified right', done => {
+    test('_getNextContentOnSide unified right', async () => {
       // Re-render as unified:
       element.viewMode = 'UNIFIED_DIFF';
-      element.render(keyLocations, prefs).then(() => {
-        builder = element._builder;
+      await element.render(keyLocations, prefs);
+      builder = element._builder;
 
-        const startElem = builder.getContentByLine(5, 'right',
-            element.$.diffTable);
-        const expectedStartString = diff.content[1].b[0];
-        const expectedNextString = diff.content[1].b[1];
-        assert.equal(startElem.textContent, expectedStartString);
+      const startElem = builder.getContentByLine(5, 'right',
+          element.$.diffTable);
+      const expectedStartString = diff.content[1].b[0];
+      const expectedNextString = diff.content[1].b[1];
+      assert.equal(startElem.textContent, expectedStartString);
 
-        const nextElem = builder._getNextContentOnSide(startElem,
-            'right');
-        assert.equal(nextElem.textContent, expectedNextString);
-
-        done();
-      });
+      const nextElem = builder._getNextContentOnSide(startElem,
+          'right');
+      assert.equal(nextElem.textContent, expectedNextString);
     });
 
     test('escaping HTML', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.js b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.js
index 3e63b0a..3b604eb 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.js
@@ -19,7 +19,7 @@
 import '../gr-diff/gr-diff.js';
 import './gr-diff-cursor.js';
 import {html} from '@polymer/polymer/lib/utils/html-tag.js';
-import {listenOnce} from '../../../test/test-utils.js';
+import {listenOnce, mockPromise} from '../../../test/test-utils.js';
 import {getMockDiffResponse} from '../../../test/mocks/diff-response.js';
 import {createDefaultDiffPrefs} from '../../../constants/constants.js';
 import {GrDiffCursor} from './gr-diff-cursor.js';
@@ -33,7 +33,7 @@
   let diffElement;
   let diff;
 
-  setup(done => {
+  setup(async () => {
     diffElement = basicFixture.instantiate();
     cursor = new GrDiffCursor();
 
@@ -48,17 +48,19 @@
       meta: {patchRange: undefined},
     };
     diffElement.path = 'some/path.ts';
+    const promise = mockPromise();
     const setupDone = () => {
       cursor._updateStops();
       cursor.moveToFirstChunk();
       diffElement.removeEventListener('render', setupDone);
-      done();
+      promise.resolve();
     };
     diffElement.addEventListener('render', setupDone);
 
     diff = getMockDiffResponse();
     diffElement.prefs = createDefaultDiffPrefs();
     diffElement.diff = diff;
+    await promise;
   });
 
   test('diff cursor functionality (side-by-side)', () => {
@@ -215,15 +217,17 @@
   });
 
   suite('unified diff', () => {
-    setup(done => {
+    setup(async () => {
+      const promise = mockPromise();
       // We must allow the diff to re-render after setting the viewMode.
       const renderHandler = function() {
         diffElement.removeEventListener('render', renderHandler);
         cursor.reInitCursor();
-        done();
+        promise.resolve();
       };
       diffElement.addEventListener('render', renderHandler);
       diffElement.viewMode = 'UNIFIED_DIFF';
+      await promise;
     });
 
     test('diff cursor functionality (unified)', () => {
@@ -312,11 +316,12 @@
   });
 
   suite('moved chunks without line range)', () => {
-    setup(done => {
+    setup(async () => {
+      const promise = mockPromise();
       const renderHandler = function() {
         diffElement.removeEventListener('render', renderHandler);
         cursor.reInitCursor();
-        done();
+        promise.resolve();
       };
       diffElement.addEventListener('render', renderHandler);
       diffElement.diff = {...diff, content: [
@@ -352,6 +357,7 @@
           ],
         },
       ]};
+      await promise;
     });
 
     test('renders moveControls with simple descriptions', () => {
@@ -363,11 +369,12 @@
   });
 
   suite('moved chunks (moveDetails)', () => {
-    setup(done => {
+    setup(async () => {
+      const promise = mockPromise();
       const renderHandler = function() {
         diffElement.removeEventListener('render', renderHandler);
         cursor.reInitCursor();
-        done();
+        promise.resolve();
       };
       diffElement.addEventListener('render', renderHandler);
       diffElement.diff = {...diff, content: [
@@ -403,6 +410,7 @@
           ],
         },
       ]};
+      await promise;
     });
 
     test('renders moveControls with simple descriptions', () => {
@@ -412,37 +420,41 @@
       assert.equal(movedOut.textContent, 'Moved to lines 2 - 4');
     });
 
-    test('startLineAnchor of movedIn chunk fires events', done => {
+    test('startLineAnchor of movedIn chunk fires events', async () => {
       const [movedIn] = diffElement.root
           .querySelectorAll('.dueToMove .moveControls');
       const [startLineAnchor] = movedIn.querySelectorAll('a');
 
+      const promise = mockPromise();
       const onMovedLinkClicked = e => {
         assert.deepEqual(e.detail, {lineNum: 4, side: 'left'});
-        done();
+        promise.resolve();
       };
       assert.equal(startLineAnchor.textContent, '4');
       startLineAnchor
           .addEventListener('moved-link-clicked', onMovedLinkClicked);
       MockInteractions.click(startLineAnchor);
+      await promise;
     });
 
-    test('endLineAnchor of movedOut fires events', done => {
+    test('endLineAnchor of movedOut fires events', async () => {
       const [, movedOut] = diffElement.root
           .querySelectorAll('.dueToMove .moveControls');
       const [, endLineAnchor] = movedOut.querySelectorAll('a');
 
+      const promise = mockPromise();
       const onMovedLinkClicked = e => {
         assert.deepEqual(e.detail, {lineNum: 4, side: 'right'});
-        done();
+        promise.resolve();
       };
       assert.equal(endLineAnchor.textContent, '4');
       endLineAnchor.addEventListener('moved-link-clicked', onMovedLinkClicked);
       MockInteractions.click(endLineAnchor);
+      await promise;
     });
   });
 
-  test('initialLineNumber not provided', done => {
+  test('initialLineNumber not provided', async () => {
     let scrollBehaviorDuringMove;
     const moveToNumStub = sinon.stub(cursor, 'moveToLineNumber');
     const moveToChunkStub = sinon.stub(cursor, 'moveToFirstChunk')
@@ -450,6 +462,7 @@
           scrollBehaviorDuringMove = cursor.cursorManager.scrollMode;
         });
 
+    const promise = mockPromise();
     function renderHandler() {
       diffElement.removeEventListener('render', renderHandler);
       cursor.reInitCursor();
@@ -457,19 +470,21 @@
       assert.isTrue(moveToChunkStub.called);
       assert.equal(scrollBehaviorDuringMove, 'never');
       assert.equal(cursor.cursorManager.scrollMode, 'keep-visible');
-      done();
+      promise.resolve();
     }
     diffElement.addEventListener('render', renderHandler);
     diffElement._diffChanged(getMockDiffResponse());
+    await promise;
   });
 
-  test('initialLineNumber provided', done => {
+  test('initialLineNumber provided', async () => {
     let scrollBehaviorDuringMove;
     const moveToNumStub = sinon.stub(cursor, 'moveToLineNumber')
         .callsFake(() => {
           scrollBehaviorDuringMove = cursor.cursorManager.scrollMode;
         });
     const moveToChunkStub = sinon.stub(cursor, 'moveToFirstChunk');
+    const promise = mockPromise();
     function renderHandler() {
       diffElement.removeEventListener('render', renderHandler);
       cursor.reInitCursor();
@@ -479,13 +494,14 @@
       assert.equal(moveToNumStub.lastCall.args[1], 'right');
       assert.equal(scrollBehaviorDuringMove, 'keep-visible');
       assert.equal(cursor.cursorManager.scrollMode, 'keep-visible');
-      done();
+      promise.resolve();
     }
     diffElement.addEventListener('render', renderHandler);
     cursor.initialLineNumber = 10;
     cursor.side = 'right';
 
     diffElement._diffChanged(getMockDiffResponse());
+    await promise;
   });
 
   test('getTargetDiffElement', () => {
@@ -502,31 +518,35 @@
       diffElement.loggedIn = true;
     });
 
-    test('adds new draft for selected line on the left', done => {
+    test('adds new draft for selected line on the left', async () => {
       cursor.moveToLineNumber(2, 'left');
+      const promise = mockPromise();
       diffElement.addEventListener('create-comment', e => {
         const {lineNum, range, side} = e.detail;
         assert.equal(lineNum, 2);
         assert.equal(range, undefined);
         assert.equal(side, 'left');
-        done();
+        promise.resolve();
       });
       cursor.createCommentInPlace();
+      await promise;
     });
 
-    test('adds draft for selected line on the right', done => {
+    test('adds draft for selected line on the right', async () => {
       cursor.moveToLineNumber(4, 'right');
+      const promise = mockPromise();
       diffElement.addEventListener('create-comment', e => {
         const {lineNum, range, side} = e.detail;
         assert.equal(lineNum, 4);
         assert.equal(range, undefined);
         assert.equal(side, 'right');
-        done();
+        promise.resolve();
       });
       cursor.createCommentInPlace();
+      await promise;
     });
 
-    test('creates comment for range if selected', done => {
+    test('creates comment for range if selected', async () => {
       const someRange = {
         start_line: 2,
         start_character: 3,
@@ -537,14 +557,16 @@
         side: 'right',
         range: someRange,
       };
+      const promise = mockPromise();
       diffElement.addEventListener('create-comment', e => {
         const {lineNum, range, side} = e.detail;
         assert.equal(lineNum, 6);
         assert.equal(range, someRange);
         assert.equal(side, 'right');
-        done();
+        promise.resolve();
       });
       cursor.createCommentInPlace();
+      await promise;
     });
 
     test('ignores call if nothing is selected', () => {
@@ -596,15 +618,13 @@
     assert.equal(cursor._findRowByNumberAndFile(5, 'left'), row);
   });
 
-  test('expand context updates stops', done => {
+  test('expand context updates stops', async () => {
     sinon.spy(cursor, '_updateStops');
     MockInteractions.tap(diffElement.shadowRoot
         .querySelector('gr-context-controls').shadowRoot
         .querySelector('.showContext'));
-    flush(() => {
-      assert.isTrue(cursor._updateStops.called);
-      done();
-    });
+    await flush();
+    assert.isTrue(cursor._updateStops.called);
   });
 
   test('updates stops when loading changes', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
index 42aa160..344f9d8 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
@@ -23,7 +23,11 @@
 import {Side, createDefaultDiffPrefs} from '../../../constants/constants.js';
 import {createChange} from '../../../test/test-data-generators.js';
 import {CoverageType} from '../../../types/types.js';
-import {addListenerForTest, stubRestApi} from '../../../test/test-utils.js';
+import {
+  addListenerForTest,
+  mockPromise,
+  stubRestApi,
+} from '../../../test/test-utils.js';
 import {EditPatchSetNum, ParentPatchSetNum} from '../../../types/common.js';
 import {_testOnly_resetState} from '../../../services/comments/comments-model.js';
 
@@ -64,14 +68,13 @@
   });
 
   suite('render reporting', () => {
-    test('starts total and content timer on render-start', done => {
+    test('starts total and content timer on render-start', () => {
       element.dispatchEvent(
           new CustomEvent('render-start', {bubbles: true, composed: true}));
       assert.isTrue(element.reporting.time.calledWithExactly(
           'Diff Total Render'));
       assert.isTrue(element.reporting.time.calledWithExactly(
           'Diff Content Render'));
-      done();
     });
 
     test('ends content timer on render-content', () => {
@@ -215,25 +218,23 @@
     });
   });
 
-  test('prefetch getDiff', done => {
+  test('prefetch getDiff', async () => {
     const diffRestApiStub = stubRestApi('getDiff')
         .returns(Promise.resolve({content: []}));
     element.changeNum = 123;
     element.patchRange = {basePatchNum: 1, patchNum: 2};
     element.path = 'file.txt';
     element.prefetchDiff();
-    element._getDiff().then(() =>{
-      assert.isTrue(diffRestApiStub.calledOnce);
-      done();
-    });
+    await element._getDiff();
+    assert.isTrue(diffRestApiStub.calledOnce);
   });
 
-  test('_getDiff handles null diff responses', done => {
+  test('_getDiff handles null diff responses', async () => {
     stubRestApi('getDiff').returns(Promise.resolve(null));
     element.changeNum = 123;
     element.patchRange = {basePatchNum: 1, patchNum: 2};
     element.path = 'file.txt';
-    element._getDiff().then(done);
+    await element._getDiff();
   });
 
   test('reload resolves on error', () => {
@@ -311,7 +312,7 @@
       };
     });
 
-    test('renders image diffs with same file name', done => {
+    test('renders image diffs with same file name', async () => {
       const mockDiff = {
         meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg', lines: 66},
         meta_b: {name: 'carrot.jpg', content_type: 'image/jpeg',
@@ -342,6 +343,7 @@
         },
       }));
 
+      const promise = mockPromise();
       const rendered = () => {
         // Recognizes that it should be an image diff.
         assert.isTrue(element.isImageDiff);
@@ -377,7 +379,7 @@
           leftLoaded = true;
           if (rightLoaded) {
             element.removeEventListener('render', rendered);
-            done();
+            promise.resolve();
           }
         });
 
@@ -390,7 +392,7 @@
           rightLoaded = true;
           if (leftLoaded) {
             element.removeEventListener('render', rendered);
-            done();
+            promise.resolve();
           }
         });
       };
@@ -398,9 +400,10 @@
       element.addEventListener('render', rendered);
       element.prefs = createDefaultDiffPrefs();
       element.reload();
+      await promise;
     });
 
-    test('renders image diffs with a different file name', done => {
+    test('renders image diffs with a different file name', async () => {
       const mockDiff = {
         meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg', lines: 66},
         meta_b: {name: 'carrot2.jpg', content_type: 'image/jpeg',
@@ -431,6 +434,7 @@
         },
       }));
 
+      const promise = mockPromise();
       const rendered = () => {
         // Recognizes that it should be an image diff.
         assert.isTrue(element.isImageDiff);
@@ -468,7 +472,7 @@
           leftLoaded = true;
           if (rightLoaded) {
             element.removeEventListener('render', rendered);
-            done();
+            promise.resolve();
           }
         });
 
@@ -481,7 +485,7 @@
           rightLoaded = true;
           if (leftLoaded) {
             element.removeEventListener('render', rendered);
-            done();
+            promise.resolve();
           }
         });
       };
@@ -489,9 +493,10 @@
       element.addEventListener('render', rendered);
       element.prefs = createDefaultDiffPrefs();
       element.reload();
+      await promise;
     });
 
-    test('renders added image', done => {
+    test('renders added image', async () => {
       const mockDiff = {
         meta_b: {name: 'carrot.jpg', content_type: 'image/jpeg',
           lines: 560},
@@ -517,6 +522,7 @@
         },
       }));
 
+      const promise = mockPromise();
       element.addEventListener('render', () => {
         // Recognizes that it should be an image diff.
         assert.isTrue(element.isImageDiff);
@@ -530,14 +536,15 @@
 
         assert.isNotOk(leftImage);
         assert.isOk(rightImage);
-        done();
+        promise.resolve();
       });
 
       element.prefs = createDefaultDiffPrefs();
       element.reload();
+      await promise;
     });
 
-    test('renders removed image', done => {
+    test('renders removed image', async () => {
       const mockDiff = {
         meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg',
           lines: 560},
@@ -563,6 +570,7 @@
         revisionImage: null,
       }));
 
+      const promise = mockPromise();
       element.addEventListener('render', () => {
         // Recognizes that it should be an image diff.
         assert.isTrue(element.isImageDiff);
@@ -576,14 +584,15 @@
 
         assert.isOk(leftImage);
         assert.isNotOk(rightImage);
-        done();
+        promise.resolve();
       });
 
       element.prefs = createDefaultDiffPrefs();
       element.reload();
+      await promise;
     });
 
-    test('does not render disallowed image type', done => {
+    test('does not render disallowed image type', async () => {
       const mockDiff = {
         meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg-evil',
           lines: 560},
@@ -611,6 +620,7 @@
         revisionImage: null,
       }));
 
+      const promise = mockPromise();
       element.addEventListener('render', () => {
         // Recognizes that it should be an image diff.
         assert.isTrue(element.isImageDiff);
@@ -619,11 +629,12 @@
         const leftImage =
             element.$.diff.$.diffTable.querySelector('td.left img');
         assert.isNotOk(leftImage);
-        done();
+        promise.resolve();
       });
 
       element.prefs = createDefaultDiffPrefs();
       element.reload();
+      await promise;
     });
   });
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
index 033b886..d9c4ba2 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.js
@@ -678,23 +678,21 @@
       assert.isNotOk(args[3]);
     });
 
-    test('A fires an error event when not logged in', done => {
+    test('A fires an error event when not logged in', async () => {
       const changeNavStub = sinon.stub(GerritNav, 'navigateToChange');
       sinon.stub(element, '_getLoggedIn').returns(Promise.resolve(false));
       const loggedInErrorSpy = sinon.spy();
       element.addEventListener('show-auth-required', loggedInErrorSpy);
       MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
-      flush(() => {
-        assert.isTrue(changeNavStub.notCalled, 'The `a` keyboard shortcut ' +
-          'should only work when the user is logged in.');
-        assert.isNull(window.sessionStorage.getItem(
-            'changeView.showReplyDialog'));
-        assert.isTrue(loggedInErrorSpy.called);
-        done();
-      });
+      await flush();
+      assert.isTrue(changeNavStub.notCalled, 'The `a` keyboard shortcut ' +
+        'should only work when the user is logged in.');
+      assert.isNull(window.sessionStorage.getItem(
+          'changeView.showReplyDialog'));
+      assert.isTrue(loggedInErrorSpy.called);
     });
 
-    test('A navigates to change with logged in', done => {
+    test('A navigates to change with logged in', async () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 5,
@@ -712,41 +710,38 @@
       const loggedInErrorSpy = sinon.spy();
       element.addEventListener('show-auth-required', loggedInErrorSpy);
       MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
-      flush(() => {
-        assert.isTrue(element.changeViewState.showReplyDialog);
-        assert(changeNavStub.lastCall.calledWithExactly(element._change, 10,
-            5), 'Should navigate to /c/42/5..10');
-        assert.isFalse(loggedInErrorSpy.called);
-        done();
-      });
+      await flush();
+      assert.isTrue(element.changeViewState.showReplyDialog);
+      assert(changeNavStub.lastCall.calledWithExactly(element._change, 10,
+          5), 'Should navigate to /c/42/5..10');
+      assert.isFalse(loggedInErrorSpy.called);
     });
 
-    test('A navigates to change with old patch number with logged in', done => {
-      element._changeNum = '42';
-      element._patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1,
-      };
-      element._change = {
-        _number: 42,
-        revisions: {
-          a: {_number: 1, commit: {parents: []}},
-          b: {_number: 2, commit: {parents: []}},
-        },
-      };
-      const changeNavStub = sinon.stub(GerritNav, 'navigateToChange');
-      sinon.stub(element, '_getLoggedIn').returns(Promise.resolve(true));
-      const loggedInErrorSpy = sinon.spy();
-      element.addEventListener('show-auth-required', loggedInErrorSpy);
-      MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
-      flush(() => {
-        assert.isTrue(element.changeViewState.showReplyDialog);
-        assert(changeNavStub.lastCall.calledWithExactly(element._change, 1,
-            PARENT), 'Should navigate to /c/42/1');
-        assert.isFalse(loggedInErrorSpy.called);
-        done();
-      });
-    });
+    test('A navigates to change with old patch number with logged in',
+        async () => {
+          element._changeNum = '42';
+          element._patchRange = {
+            basePatchNum: PARENT,
+            patchNum: 1,
+          };
+          element._change = {
+            _number: 42,
+            revisions: {
+              a: {_number: 1, commit: {parents: []}},
+              b: {_number: 2, commit: {parents: []}},
+            },
+          };
+          const changeNavStub = sinon.stub(GerritNav, 'navigateToChange');
+          sinon.stub(element, '_getLoggedIn').returns(Promise.resolve(true));
+          const loggedInErrorSpy = sinon.spy();
+          element.addEventListener('show-auth-required', loggedInErrorSpy);
+          MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
+          await flush();
+          assert.isTrue(element.changeViewState.showReplyDialog);
+          assert(changeNavStub.lastCall.calledWithExactly(element._change, 1,
+              PARENT), 'Should navigate to /c/42/1');
+          assert.isFalse(loggedInErrorSpy.called);
+        });
 
     test('keyboard shortcuts with patch range', () => {
       element._changeNum = '42';
@@ -860,7 +855,7 @@
       assert.isTrue(changeNavStub.calledOnce);
     });
 
-    test('edit should redirect to edit page', done => {
+    test('edit should redirect to edit page', async () => {
       element._loggedIn = true;
       element._path = 't.txt';
       element._patchRange = {
@@ -877,23 +872,21 @@
         },
       };
       const redirectStub = sinon.stub(GerritNav, 'navigateToRelativeUrl');
-      flush(() => {
-        const editBtn = element.shadowRoot
-            .querySelector('.editButton gr-button');
-        assert.isTrue(!!editBtn);
-        MockInteractions.tap(editBtn);
-        assert.isTrue(redirectStub.called);
-        assert.isTrue(redirectStub.lastCall.calledWithExactly(
-            GerritNav.getEditUrlForDiff(
-                element._change,
-                element._path,
-                element._patchRange.patchNum
-            )));
-        done();
-      });
+      await flush();
+      const editBtn = element.shadowRoot
+          .querySelector('.editButton gr-button');
+      assert.isTrue(!!editBtn);
+      MockInteractions.tap(editBtn);
+      assert.isTrue(redirectStub.called);
+      assert.isTrue(redirectStub.lastCall.calledWithExactly(
+          GerritNav.getEditUrlForDiff(
+              element._change,
+              element._path,
+              element._patchRange.patchNum
+          )));
     });
 
-    test('edit should redirect to edit page with line number', done => {
+    test('edit should redirect to edit page with line number', async () => {
       const lineNumber = 42;
       element._loggedIn = true;
       element._path = 't.txt';
@@ -913,21 +906,19 @@
       sinon.stub(element.cursor, 'getAddress')
           .returns({number: lineNumber, isLeftSide: false});
       const redirectStub = sinon.stub(GerritNav, 'navigateToRelativeUrl');
-      flush(() => {
-        const editBtn = element.shadowRoot
-            .querySelector('.editButton gr-button');
-        assert.isTrue(!!editBtn);
-        MockInteractions.tap(editBtn);
-        assert.isTrue(redirectStub.called);
-        assert.isTrue(redirectStub.lastCall.calledWithExactly(
-            GerritNav.getEditUrlForDiff(
-                element._change,
-                element._path,
-                element._patchRange.patchNum,
-                lineNumber
-            )));
-        done();
-      });
+      await flush();
+      const editBtn = element.shadowRoot
+          .querySelector('.editButton gr-button');
+      assert.isTrue(!!editBtn);
+      MockInteractions.tap(editBtn);
+      assert.isTrue(redirectStub.called);
+      assert.isTrue(redirectStub.lastCall.calledWithExactly(
+          GerritNav.getEditUrlForDiff(
+              element._change,
+              element._path,
+              element._patchRange.patchNum,
+              lineNumber
+          )));
     });
 
     function isEditVisibile({loggedIn, changeStatus}) {
@@ -1294,7 +1285,7 @@
       assert.isFalse(saveReviewedStub.called);
     });
 
-    test('hash is determined from params', done => {
+    test('hash is determined from params', async () => {
       sinon.stub(element.$.diffHost, 'reload');
       sinon.stub(element, '_initLineOfInterestAndCursor');
 
@@ -1308,10 +1299,8 @@
         hash: 10,
       };
 
-      flush(() => {
-        assert.isTrue(element._initLineOfInterestAndCursor.calledOnce);
-        done();
-      });
+      await flush();
+      assert.isTrue(element._initLineOfInterestAndCursor.calledOnce);
     });
 
     test('diff mode selector correctly toggles the diff', () => {
@@ -1360,15 +1349,13 @@
       assert.equal(element._getDiffViewMode(), 'SIDE_BY_SIDE');
     });
 
-    test('diff mode selector should be hidden for binary', done => {
+    test('diff mode selector should be hidden for binary', async () => {
       element._diff = {binary: true, content: []};
 
-      flush(() => {
-        const diffModeSelector = element.shadowRoot
-            .querySelector('.diffModeSelector');
-        assert.isTrue(diffModeSelector.classList.contains('hide'));
-        done();
-      });
+      await flush();
+      const diffModeSelector = element.shadowRoot
+          .querySelector('.diffModeSelector');
+      assert.isTrue(diffModeSelector.classList.contains('hide'));
     });
 
     suite('_commitRange', () => {
@@ -1400,7 +1387,7 @@
             change));
       });
 
-      test('uses the patchNum and basePatchNum ', done => {
+      test('uses the patchNum and basePatchNum ', async () => {
         element.params = {
           view: GerritNav.View.DIFF,
           changeNum: '42',
@@ -1409,16 +1396,14 @@
           path: '/COMMIT_MSG',
         };
         element._change = change;
-        flush(() => {
-          assert.deepEqual(element._commitRange, {
-            baseCommit: 'commit-sha-2',
-            commit: 'commit-sha-4',
-          });
-          done();
+        await flush();
+        assert.deepEqual(element._commitRange, {
+          baseCommit: 'commit-sha-2',
+          commit: 'commit-sha-4',
         });
       });
 
-      test('uses the parent when there is no base patch num ', done => {
+      test('uses the parent when there is no base patch num ', async () => {
         element.params = {
           view: GerritNav.View.DIFF,
           changeNum: '42',
@@ -1426,12 +1411,10 @@
           path: '/COMMIT_MSG',
         };
         element._change = change;
-        flush(() => {
-          assert.deepEqual(element._commitRange, {
-            commit: 'commit-sha-5',
-            baseCommit: 'sha-5-parent',
-          });
-          done();
+        await flush();
+        assert.deepEqual(element._commitRange, {
+          commit: 'commit-sha-5',
+          baseCommit: 'sha-5-parent',
         });
       });
     });
@@ -1921,7 +1904,7 @@
       ]);
     });
 
-    test('File change should trigger navigateToDiff once', done => {
+    test('File change should trigger navigateToDiff once', async () => {
       element._files = getFilesFromFileList(['file1', 'file2', 'file3']);
       sinon.stub(element, '_initLineOfInterestAndCursor');
       sinon.stub(GerritNav, 'navigateToDiff');
@@ -1942,7 +1925,7 @@
         ...createChange(),
         revisions: createRevisions(1),
       };
-      flush();
+      await flush();
       assert.isTrue(GerritNav.navigateToDiff.notCalled);
 
       // Switch to file2
@@ -1964,7 +1947,6 @@
 
       // No extra call
       assert.isTrue(GerritNav.navigateToDiff.calledOnce);
-      done();
     });
 
     test('_computeDownloadDropdownLinks', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.js
index c59ceb7..9ee779c 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.js
@@ -23,7 +23,7 @@
 import {_setHiddenScroll} from '../../../scripts/hiddenscroll.js';
 import {runA11yAudit} from '../../../test/a11y-test-utils.js';
 import '@polymer/paper-button/paper-button.js';
-import {stubRestApi} from '../../../test/test-utils.js';
+import {mockPromise, stubRestApi} from '../../../test/test-utils.js';
 
 const basicFixture = fixtureFromElement('gr-diff');
 
@@ -232,7 +232,9 @@
         };
       });
 
-      test('renders image diffs with same file name', done => {
+      test('renders image diffs with same file name', async () => {
+        const leftRendered = mockPromise();
+        const rightRendered = mockPromise();
         const rendered = () => {
           // Recognizes that it should be an image diff.
           assert.isTrue(element.isImageDiff);
@@ -256,19 +258,12 @@
           assert.isNotOk(rightLabelName);
           assert.isNotOk(leftLabelName);
 
-          let leftLoaded = false;
-          let rightLoaded = false;
-
           leftImage.addEventListener('load', () => {
             assert.isOk(leftImage);
             assert.equal(leftImage.getAttribute('src'),
                 'data:image/bmp;base64,' + mockFile1.body);
             assert.equal(leftLabelContent.textContent, '1\u00d71 image/bmp');// \u00d7 - '×'
-            leftLoaded = true;
-            if (rightLoaded) {
-              element.removeEventListener('render', rendered);
-              done();
-            }
+            leftRendered.resolve();
           });
 
           rightImage.addEventListener('load', () => {
@@ -277,11 +272,7 @@
                 'data:image/bmp;base64,' + mockFile2.body);
             assert.equal(rightLabelContent.textContent, '1\u00d71 image/bmp');// \u00d7 - '×'
 
-            rightLoaded = true;
-            if (leftLoaded) {
-              element.removeEventListener('render', rendered);
-              done();
-            }
+            rightRendered.resolve();
           });
         };
 
@@ -305,9 +296,11 @@
           content: [{skip: 66}],
           binary: true,
         };
+        await Promise.all([leftRendered, rightRendered]);
+        element.removeEventListener('render', rendered);
       });
 
-      test('renders image diffs with a different file name', done => {
+      test('renders image diffs with a different file name', async () => {
         const mockDiff = {
           meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg', lines: 66},
           meta_b: {name: 'carrot2.jpg', content_type: 'image/jpeg',
@@ -324,7 +317,8 @@
           content: [{skip: 66}],
           binary: true,
         };
-
+        const leftRendered = mockPromise();
+        const rightRendered = mockPromise();
         const rendered = () => {
           // Recognizes that it should be an image diff.
           assert.isTrue(element.isImageDiff);
@@ -350,19 +344,12 @@
           assert.equal(leftLabelName.textContent, mockDiff.meta_a.name);
           assert.equal(rightLabelName.textContent, mockDiff.meta_b.name);
 
-          let leftLoaded = false;
-          let rightLoaded = false;
-
           leftImage.addEventListener('load', () => {
             assert.isOk(leftImage);
             assert.equal(leftImage.getAttribute('src'),
                 'data:image/bmp;base64,' + mockFile1.body);
             assert.equal(leftLabelContent.textContent, '1\u00d71 image/bmp');// \u00d7 - '×'
-            leftLoaded = true;
-            if (rightLoaded) {
-              element.removeEventListener('render', rendered);
-              done();
-            }
+            leftRendered.resolve();
           });
 
           rightImage.addEventListener('load', () => {
@@ -371,11 +358,7 @@
                 'data:image/bmp;base64,' + mockFile2.body);
             assert.equal(rightLabelContent.textContent, '1\u00d71 image/bmp');// \u00d7 - '×'
 
-            rightLoaded = true;
-            if (leftLoaded) {
-              element.removeEventListener('render', rendered);
-              done();
-            }
+            rightRendered.resolve();
           });
         };
 
@@ -386,9 +369,11 @@
         element.revisionImage = mockFile2;
         element.revisionImage._name = mockDiff.meta_b.name;
         element.diff = mockDiff;
+        await Promise.all([leftRendered, rightRendered]);
+        element.removeEventListener('render', rendered);
       });
 
-      test('renders added image', done => {
+      test('renders added image', async () => {
         const mockDiff = {
           meta_b: {name: 'carrot.jpg', content_type: 'image/jpeg',
             lines: 560},
@@ -405,27 +390,27 @@
           binary: true,
         };
 
-        function rendered() {
-          // Recognizes that it should be an image diff.
-          assert.isTrue(element.isImageDiff);
-          assert.instanceOf(
-              element.$.diffBuilder._builder, GrDiffBuilderImage);
-
-          const leftImage = element.$.diffTable.querySelector('td.left img');
-          const rightImage = element.$.diffTable.querySelector('td.right img');
-
-          assert.isNotOk(leftImage);
-          assert.isOk(rightImage);
-          done();
-          element.removeEventListener('render', rendered);
-        }
+        const promise = mockPromise();
+        function rendered() { promise.resolve(); }
         element.addEventListener('render', rendered);
 
         element.revisionImage = mockFile2;
         element.diff = mockDiff;
+        await promise;
+        element.removeEventListener('render', rendered);
+        // Recognizes that it should be an image diff.
+        assert.isTrue(element.isImageDiff);
+        assert.instanceOf(
+            element.$.diffBuilder._builder, GrDiffBuilderImage);
+
+        const leftImage = element.$.diffTable.querySelector('td.left img');
+        const rightImage = element.$.diffTable.querySelector('td.right img');
+
+        assert.isNotOk(leftImage);
+        assert.isOk(rightImage);
       });
 
-      test('renders removed image', done => {
+      test('renders removed image', async () => {
         const mockDiff = {
           meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg',
             lines: 560},
@@ -441,28 +426,27 @@
           content: [{skip: 66}],
           binary: true,
         };
-
-        function rendered() {
-          // Recognizes that it should be an image diff.
-          assert.isTrue(element.isImageDiff);
-          assert.instanceOf(
-              element.$.diffBuilder._builder, GrDiffBuilderImage);
-
-          const leftImage = element.$.diffTable.querySelector('td.left img');
-          const rightImage = element.$.diffTable.querySelector('td.right img');
-
-          assert.isOk(leftImage);
-          assert.isNotOk(rightImage);
-          done();
-          element.removeEventListener('render', rendered);
-        }
+        const promise = mockPromise();
+        function rendered() { promise.resolve(); }
         element.addEventListener('render', rendered);
 
         element.baseImage = mockFile1;
         element.diff = mockDiff;
+        await promise;
+        element.removeEventListener('render', rendered);
+        // Recognizes that it should be an image diff.
+        assert.isTrue(element.isImageDiff);
+        assert.instanceOf(
+            element.$.diffBuilder._builder, GrDiffBuilderImage);
+
+        const leftImage = element.$.diffTable.querySelector('td.left img');
+        const rightImage = element.$.diffTable.querySelector('td.right img');
+
+        assert.isOk(leftImage);
+        assert.isNotOk(rightImage);
       });
 
-      test('does not render disallowed image type', done => {
+      test('does not render disallowed image type', async () => {
         const mockDiff = {
           meta_a: {name: 'carrot.jpg', content_type: 'image/jpeg-evil',
             lines: 560},
@@ -480,50 +464,54 @@
         };
         mockFile1.type = 'image/jpeg-evil';
 
-        function rendered() {
-          // Recognizes that it should be an image diff.
-          assert.isTrue(element.isImageDiff);
-          assert.instanceOf(
-              element.$.diffBuilder._builder, GrDiffBuilderImage);
-          const leftImage = element.$.diffTable.querySelector('td.left img');
-          assert.isNotOk(leftImage);
-          done();
-          element.removeEventListener('render', rendered);
-        }
+        const promise = mockPromise();
+        function rendered() { promise.resolve(); }
         element.addEventListener('render', rendered);
 
         element.baseImage = mockFile1;
         element.diff = mockDiff;
+        await promise;
+        element.removeEventListener('render', rendered);
+        // Recognizes that it should be an image diff.
+        assert.isTrue(element.isImageDiff);
+        assert.instanceOf(
+            element.$.diffBuilder._builder, GrDiffBuilderImage);
+        const leftImage = element.$.diffTable.querySelector('td.left img');
+        assert.isNotOk(leftImage);
       });
     });
 
-    test('_handleTap lineNum', done => {
+    test('_handleTap lineNum', async () => {
       const addDraftStub = sinon.stub(element, 'addDraftAtLine');
       const el = document.createElement('div');
       el.className = 'lineNum';
+      const promise = mockPromise();
       el.addEventListener('click', e => {
         element._handleTap(e);
         assert.isTrue(addDraftStub.called);
         assert.equal(addDraftStub.lastCall.args[0], el);
-        done();
+        promise.resolve();
       });
       el.click();
+      await promise;
     });
 
-    test('_handleTap context', done => {
+    test('_handleTap context', async () => {
       const showContextStub =
           sinon.stub(element.$.diffBuilder, 'showContext');
       const el = document.createElement('div');
       el.className = 'showContext';
+      const promise = mockPromise();
       el.addEventListener('click', e => {
         element._handleDiffContextExpanded(e);
         assert.isTrue(showContextStub.called);
-        done();
+        promise.resolve();
       });
       el.click();
+      await promise;
     });
 
-    test('_handleTap content', done => {
+    test('_handleTap content', async () => {
       const content = document.createElement('div');
       const lineEl = document.createElement('div');
       lineEl.className = 'lineNum';
@@ -534,13 +522,15 @@
       const selectStub = sinon.stub(element, '_selectLine');
 
       content.className = 'content';
+      const promise = mockPromise();
       content.addEventListener('click', e => {
         element._handleTap(e);
         assert.isTrue(selectStub.called);
         assert.equal(selectStub.lastCall.args[0], lineEl);
-        done();
+        promise.resolve();
       });
       content.click();
+      await promise;
     });
 
     suite('getCursorStops', () => {
@@ -816,41 +806,47 @@
       element.noRenderOnPrefsChange = true;
     });
 
-    test('large render w/ context = 10', done => {
+    test('large render w/ context = 10', async () => {
       element.prefs = {...MINIMAL_PREFS, context: 10};
+      const promise = mockPromise();
       function rendered() {
         assert.isTrue(renderStub.called);
         assert.isFalse(element._showWarning);
-        done();
+        promise.resolve();
         element.removeEventListener('render', rendered);
       }
       element.addEventListener('render', rendered);
       element._renderDiffTable();
+      await promise;
     });
 
-    test('large render w/ whole file and bypass', done => {
+    test('large render w/ whole file and bypass', async () => {
       element.prefs = {...MINIMAL_PREFS, context: -1};
       element._safetyBypass = 10;
+      const promise = mockPromise();
       function rendered() {
         assert.isTrue(renderStub.called);
         assert.isFalse(element._showWarning);
-        done();
+        promise.resolve();
         element.removeEventListener('render', rendered);
       }
       element.addEventListener('render', rendered);
       element._renderDiffTable();
+      await promise;
     });
 
-    test('large render w/ whole file and no bypass', done => {
+    test('large render w/ whole file and no bypass', async () => {
       element.prefs = {...MINIMAL_PREFS, context: -1};
+      const promise = mockPromise();
       function rendered() {
         assert.isFalse(renderStub.called);
         assert.isTrue(element._showWarning);
-        done();
+        promise.resolve();
         element.removeEventListener('render', rendered);
       }
       element.addEventListener('render', rendered);
       element._renderDiffTable();
+      await promise;
     });
 
     test('toggles expand context using bypass', async () => {
@@ -1219,16 +1215,18 @@
     assert.equal(element.getDiffLength(diff), 52);
   });
 
-  test('`render` event has contentRendered field in detail', done => {
+  test('`render` event has contentRendered field in detail', async () => {
     element = basicFixture.instantiate();
     element.prefs = {};
     sinon.stub(element.$.diffBuilder, 'render')
         .returns(Promise.resolve());
+    const promise = mockPromise();
     element.addEventListener('render', event => {
       assert.isTrue(event.detail.contentRendered);
-      done();
+      promise.resolve();
     });
     element._renderDiffTable();
+    await promise;
   });
 
   test('_prefsEqual', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.js b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.js
index 89b8b4a..0fe1fe2 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.js
@@ -196,7 +196,7 @@
   });
 
   test('_computeBaseDropdownContent called when changeComments update',
-      done => {
+      async () => {
         element.revisions = [
           {commit: {parents: []}},
           {commit: {parents: []}},
@@ -212,15 +212,14 @@
         ];
         element.patchNum = 2;
         element.basePatchNum = 'PARENT';
-        flush();
+        await flush();
 
         // Should be recomputed for each available patch
         sinon.stub(element, '_computeBaseDropdownContent');
         assert.equal(element._computeBaseDropdownContent.callCount, 0);
         element.changeComments = new ChangeComments();
-        flush();
+        await flush();
         assert.equal(element._computeBaseDropdownContent.callCount, 1);
-        done();
       });
 
   test('_computePatchDropdownContent called when basePatchNum updates', () => {
diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer_test.js b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer_test.js
index b8c3c16..c907a80 100644
--- a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer_test.js
@@ -120,7 +120,7 @@
     assert.isFalse(annotationSpy.called);
   });
 
-  test('process on empty diff does nothing', done => {
+  test('process on empty diff does nothing', async () => {
     element.diff = {
       meta_a: {content_type: 'application/json'},
       meta_b: {content_type: 'application/json'},
@@ -128,17 +128,14 @@
     };
     const processNextSpy = sinon.spy(element, '_processNextLine');
 
-    const processPromise = element.process();
+    await element.process();
 
-    processPromise.then(() => {
-      assert.isFalse(processNextSpy.called);
-      assert.equal(element.baseRanges.length, 0);
-      assert.equal(element.revisionRanges.length, 0);
-      done();
-    });
+    assert.isFalse(processNextSpy.called);
+    assert.equal(element.baseRanges.length, 0);
+    assert.equal(element.revisionRanges.length, 0);
   });
 
-  test('process for unsupported languages does nothing', done => {
+  test('process for unsupported languages does nothing', async () => {
     element.diff = {
       meta_a: {content_type: 'text/x+objective-cobol-plus-plus'},
       meta_b: {content_type: 'application/not-a-real-language'},
@@ -146,33 +143,27 @@
     };
     const processNextSpy = sinon.spy(element, '_processNextLine');
 
-    const processPromise = element.process();
+    await element.process();
 
-    processPromise.then(() => {
-      assert.isFalse(processNextSpy.called);
-      assert.equal(element.baseRanges.length, 0);
-      assert.equal(element.revisionRanges.length, 0);
-      done();
-    });
+    assert.isFalse(processNextSpy.called);
+    assert.equal(element.baseRanges.length, 0);
+    assert.equal(element.revisionRanges.length, 0);
   });
 
-  test('process while disabled does nothing', done => {
+  test('process while disabled does nothing', async () => {
     const processNextSpy = sinon.spy(element, '_processNextLine');
     element.enabled = false;
     const loadHLJSSpy = sinon.spy(element, '_loadHLJS');
 
-    const processPromise = element.process();
+    await element.process();
 
-    processPromise.then(() => {
-      assert.isFalse(processNextSpy.called);
-      assert.equal(element.baseRanges.length, 0);
-      assert.equal(element.revisionRanges.length, 0);
-      assert.isFalse(loadHLJSSpy.called);
-      done();
-    });
+    assert.isFalse(processNextSpy.called);
+    assert.equal(element.baseRanges.length, 0);
+    assert.equal(element.revisionRanges.length, 0);
+    assert.isFalse(loadHLJSSpy.called);
   });
 
-  test('process highlight ipsum', done => {
+  test('process highlight ipsum', async () => {
     element.diff.meta_a.content_type = 'application/json';
     element.diff.meta_b.content_type = 'application/json';
 
@@ -180,65 +171,61 @@
     window.hljs = mockHLJS;
     const highlightSpy = sinon.spy(mockHLJS, 'highlight');
     const processNextSpy = sinon.spy(element, '_processNextLine');
-    const processPromise = element.process();
+    await element.process();
 
-    processPromise.then(() => {
-      const linesA = diff.meta_a.lines;
-      const linesB = diff.meta_b.lines;
+    const linesA = diff.meta_a.lines;
+    const linesB = diff.meta_b.lines;
 
-      assert.isTrue(processNextSpy.called);
-      assert.equal(element.baseRanges.length, linesA);
-      assert.equal(element.revisionRanges.length, linesB);
+    assert.isTrue(processNextSpy.called);
+    assert.equal(element.baseRanges.length, linesA);
+    assert.equal(element.revisionRanges.length, linesB);
 
-      assert.equal(highlightSpy.callCount, linesA + linesB);
+    assert.equal(highlightSpy.callCount, linesA + linesB);
 
-      // The first line of both sides have a range.
-      let ranges = [element.baseRanges[0], element.revisionRanges[0]];
-      for (const range of ranges) {
-        assert.equal(range.length, 1);
-        assert.equal(range[0].className,
-            'gr-diff gr-syntax gr-syntax-string');
-        assert.equal(range[0].start, 'lorem '.length);
-        assert.equal(range[0].length, 'ipsum'.length);
-      }
-
-      // There are no ranges from ll.1-12 on the left and ll.1-11 on the
-      // right.
-      ranges = element.baseRanges.slice(1, 12)
-          .concat(element.revisionRanges.slice(1, 11));
-
-      for (const range of ranges) {
-        assert.equal(range.length, 0);
-      }
-
-      // There should be another pair of ranges on l.13 for the left and
-      // l.12 for the right.
-      ranges = [element.baseRanges[13], element.revisionRanges[12]];
-
-      for (const range of ranges) {
-        assert.equal(range.length, 1);
-        assert.equal(range[0].className,
-            'gr-diff gr-syntax gr-syntax-string');
-        assert.equal(range[0].start, 32);
-        assert.equal(range[0].length, 'ipsum'.length);
-      }
-
-      // The next group should have a similar instance on either side.
-
-      let range = element.baseRanges[15];
+    // The first line of both sides have a range.
+    let ranges = [element.baseRanges[0], element.revisionRanges[0]];
+    for (const range of ranges) {
       assert.equal(range.length, 1);
-      assert.equal(range[0].className, 'gr-diff gr-syntax gr-syntax-string');
-      assert.equal(range[0].start, 34);
+      assert.equal(range[0].className,
+          'gr-diff gr-syntax gr-syntax-string');
+      assert.equal(range[0].start, 'lorem '.length);
       assert.equal(range[0].length, 'ipsum'.length);
+    }
 
-      range = element.revisionRanges[14];
+    // There are no ranges from ll.1-12 on the left and ll.1-11 on the
+    // right.
+    ranges = element.baseRanges.slice(1, 12)
+        .concat(element.revisionRanges.slice(1, 11));
+
+    for (const range of ranges) {
+      assert.equal(range.length, 0);
+    }
+
+    // There should be another pair of ranges on l.13 for the left and
+    // l.12 for the right.
+    ranges = [element.baseRanges[13], element.revisionRanges[12]];
+
+    for (const range of ranges) {
       assert.equal(range.length, 1);
-      assert.equal(range[0].className, 'gr-diff gr-syntax gr-syntax-string');
-      assert.equal(range[0].start, 35);
+      assert.equal(range[0].className,
+          'gr-diff gr-syntax gr-syntax-string');
+      assert.equal(range[0].start, 32);
       assert.equal(range[0].length, 'ipsum'.length);
+    }
 
-      done();
-    });
+    // The next group should have a similar instance on either side.
+
+    let range = element.baseRanges[15];
+    assert.equal(range.length, 1);
+    assert.equal(range[0].className, 'gr-diff gr-syntax gr-syntax-string');
+    assert.equal(range[0].start, 34);
+    assert.equal(range[0].length, 'ipsum'.length);
+
+    range = element.revisionRanges[14];
+    assert.equal(range.length, 1);
+    assert.equal(range[0].className, 'gr-diff gr-syntax gr-syntax-string');
+    assert.equal(range[0].start, 35);
+    assert.equal(range[0].length, 'ipsum'.length);
   });
 
   test('init calls cancel', () => {