diff --git a/test/spec/ol/interaction/draganddrop.test.js b/test/spec/ol/interaction/draganddrop.test.js
index de6dd8cf49..0cd429eeb6 100644
--- a/test/spec/ol/interaction/draganddrop.test.js
+++ b/test/spec/ol/interaction/draganddrop.test.js
@@ -1,4 +1,3 @@
-import {inherits} from '../../../../src/ol/index.js';
 import View from '../../../../src/ol/View.js';
 import Event from '../../../../src/ol/events/Event.js';
 import EventTarget from '../../../../src/ol/events/EventTarget.js';
@@ -94,14 +93,16 @@ where('FileReader').describe('ol.interaction.DragAndDrop', function() {
     beforeEach(function() {
       OrigFileReader = FileReader;
 
-      FileReader = function() {
-        EventTarget.apply(this, arguments);
-        this.readAsText = function(file) {
+      class MockFileReader extends EventTarget {
+        constructor() {
+          super(...arguments);
+        }
+        readAsText(file) {
           this.result = file;
           this.dispatchEvent('load');
-        };
-      };
-      inherits(FileReader, EventTarget);
+        }
+      }
+      FileReader = MockFileReader;
     });
 
     afterEach(function() {
diff --git a/test/spec/ol/renderer/canvas/vectortilelayer.test.js b/test/spec/ol/renderer/canvas/vectortilelayer.test.js
index 1ddfe46f6f..909ea2989a 100644
--- a/test/spec/ol/renderer/canvas/vectortilelayer.test.js
+++ b/test/spec/ol/renderer/canvas/vectortilelayer.test.js
@@ -59,14 +59,15 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
       feature2 = new Feature(new Point([0, 0]));
       feature3 = new RenderFeature('Point', [1, -1], []);
       feature2.setStyle(featureStyle);
-      const TileClass = function() {
-        VectorTile.apply(this, arguments);
-        this.setState(TileState.LOADED);
-        this.setFeatures([feature1, feature2, feature3]);
-        this.setProjection(getProjection('EPSG:4326'));
-        tileCallback(this);
-      };
-      inherits(TileClass, VectorTile);
+      class TileClass extends VectorTile {
+        constructor() {
+          super(...arguments);
+          this.setState(TileState.LOADED);
+          this.setFeatures([feature1, feature2, feature3]);
+          this.setProjection(getProjection('EPSG:4326'));
+          tileCallback(this);
+        }
+      }
       source = new VectorTileSource({
         format: new MVT(),
         tileClass: TileClass,
@@ -291,23 +292,24 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
 
   describe('#forEachFeatureAtCoordinate', function() {
     let layer, renderer, replayGroup;
-    const TileClass = function() {
-      VectorImageTile.apply(this, arguments);
-      this.extent = [-Infinity, -Infinity, Infinity, Infinity];
-      this.setState(TileState.LOADED);
-      const sourceTile = new VectorTile([0, 0, 0]);
-      sourceTile.setState(TileState.LOADED);
-      sourceTile.setProjection(getProjection('EPSG:3857'));
-      sourceTile.getReplayGroup = function() {
-        return replayGroup;
-      };
-      const key = sourceTile.tileCoord.toString();
-      this.tileKeys = [key];
-      this.sourceTiles_ = {};
-      this.sourceTiles_[key] = sourceTile;
-      this.wrappedTileCoord = arguments[0];
-    };
-    inherits(TileClass, VectorImageTile);
+    class TileClass extends VectorImageTile {
+      constructor() {
+        super(...arguments);
+        this.extent = [-Infinity, -Infinity, Infinity, Infinity];
+        this.setState(TileState.LOADED);
+        const sourceTile = new VectorTile([0, 0, 0]);
+        sourceTile.setState(TileState.LOADED);
+        sourceTile.setProjection(getProjection('EPSG:3857'));
+        sourceTile.getReplayGroup = function() {
+          return replayGroup;
+        };
+        const key = sourceTile.tileCoord.toString();
+        this.tileKeys = [key];
+        this.sourceTiles_ = {};
+        this.sourceTiles_[key] = sourceTile;
+        this.wrappedTileCoord = arguments[0];
+      }
+    }
 
     beforeEach(function() {
       replayGroup = {};
diff --git a/test/spec/ol/source/tile.test.js b/test/spec/ol/source/tile.test.js
index 0a46e6dc85..b8b14bbb51 100644
--- a/test/spec/ol/source/tile.test.js
+++ b/test/spec/ol/source/tile.test.js
@@ -1,4 +1,3 @@
-import {inherits} from '../../../../src/ol/index.js';
 import Tile from '../../../../src/ol/Tile.js';
 import TileRange from '../../../../src/ol/TileRange.js';
 import {get as getProjection} from '../../../../src/ol/proj.js';
@@ -16,24 +15,24 @@ import TileGrid from '../../../../src/ol/tilegrid/TileGrid.js';
  * @param {Object.<string, ol.TileState>} tileStates Lookup of tile key to
  *     tile state.
  */
-const MockTile = function(tileStates) {
-  const tileGrid = new TileGrid({
-    resolutions: [360 / 256, 180 / 256, 90 / 256, 45 / 256],
-    origin: [-180, -180],
-    tileSize: 256
-  });
+class MockTile extends TileSource {
+  constructor(tileStates) {
+    const tileGrid = new TileGrid({
+      resolutions: [360 / 256, 180 / 256, 90 / 256, 45 / 256],
+      origin: [-180, -180],
+      tileSize: 256
+    });
 
-  TileSource.call(this, {
-    projection: getProjection('EPSG:4326'),
-    tileGrid: tileGrid
-  });
+    super({
+      projection: getProjection('EPSG:4326'),
+      tileGrid: tileGrid
+    });
 
-  for (const key in tileStates) {
-    this.tileCache.set(key, new Tile(key.split('/'), tileStates[key]));
+    for (const key in tileStates) {
+      this.tileCache.set(key, new Tile(key.split('/'), tileStates[key]));
+    }
   }
-
-};
-inherits(MockTile, TileSource);
+}
 
 
 /**