Transpile sources for testing

src/ol/AssertionError.js

@@ -35,6 +35,8 @@ class AssertionError extends Error {
      */
     this.name = 'AssertionError';
 
+    // Re-assign message, see https://github.com/Rich-Harris/buble/issues/40
+    this.message = message;
   }
 
 }

test/karma.config.js

@@ -60,7 +60,17 @@ module.exports = function(karma) {
     reporters: ['progress'],
     webpack: {
       devtool: 'inline-source-map',
-      mode: 'development'
+      mode: 'development',
+      module: {
+        rules: [
+          {
+            test: /\.js$/,
+            use: {
+              loader: 'buble-loader'
+            }
+          }
+        ]
+      }
     },
     webpackMiddleware: {
       noInfo: true

test/spec/ol/assertionerror.test.js

@@ -22,4 +22,11 @@ describe('ol.AssertionError', function() {
     const error = new AssertionError(42);
     expect(error.name).to.be('AssertionError');
   });
+
+  it('is instanceof Error and AssertionError', function() {
+    const error = new AssertionError(42);
+    expect(error instanceof Error).to.be(true);
+    expect(error instanceof AssertionError).to.be(true);
+  });
+
 });