Load source maps of dependencies for tests

test/browser/karma.config.cjs

@@ -74,6 +74,11 @@ module.exports = function (karma) {
       },
       module: {
         rules: [
+          {
+            test: /\.js$/,
+            enforce: 'pre',
+            use: ['source-map-loader'],
+          },
           {
             test: /\.js$/,
             use: {

test/browser/spec/ol/layer/MapboxVector.test.js

@@ -1,6 +1,5 @@
 import MapboxVectorLayer from '../../../../../src/ol/layer/MapboxVector.js';
 import {asString} from '../../../../../src/ol/color.js';
-import {strokeInstruction} from '../../../../../src/ol/render/canvas/Instruction.js';
 import {unByKey} from '../../../../../src/ol/Observable.js';
 
 describe('ol/layer/MapboxVector', () => {