1 files changed, 71 insertions, 0 deletions
diff --git a/spec/frontend/__helpers__/web_worker_fake.js b/spec/frontend/__helpers__/web_worker_fake.js
new file mode 100644
index 00000000000..041a9bd8540
--- /dev/null
+++ b/spec/frontend/__helpers__/web_worker_fake.js
@@ -0,0 +1,71 @@
+import path from 'path';
+
+const isRelative = (pathArg) => pathArg.startsWith('.');
+
+const transformRequirePath = (base, pathArg) => {
+  if (!isRelative(pathArg)) {
+    return pathArg;
+  }
+
+  return path.resolve(base, pathArg);
+};
+
+const createRelativeRequire = (filename) => {
+  const rel = path.relative(__dirname, path.dirname(filename));
+  const base = path.resolve(__dirname, rel);
+
+  // reason: Dynamic require should be fine here since the code is dynamically evaluated anyways.
+  // eslint-disable-next-line import/no-dynamic-require, global-require
+  return (pathArg) => require(transformRequirePath(base, pathArg));
+};
+
+/**
+ * Simulates a WebWorker module similar to the kind created by Webpack's [`worker-loader`][1]
+ *
+ * [1]: https://webpack.js.org/loaders/worker-loader/
+ */
+export class FakeWebWorker {
+  /**
+   * Constructs a new FakeWebWorker instance
+   *
+   * @param {String} filename is the full path of the code, which is used to resolve relative imports.
+   * @param {String} code is the raw code of the web worker, which is dynamically evaluated on construction.
+   */
+  constructor(filename, code) {
+    let isAlive = true;
+
+    const clientTarget = new EventTarget();
+    const workerTarget = new EventTarget();
+
+    this.addEventListener = (...args) => clientTarget.addEventListener(...args);
+    this.removeEventListener = (...args) => clientTarget.removeEventListener(...args);
+    this.postMessage = (message) => {
+      if (!isAlive) {
+        return;
+      }
+
+      workerTarget.dispatchEvent(new MessageEvent('message', { data: message }));
+    };
+    this.terminate = () => {
+      isAlive = false;
+    };
+
+    const workerScope = {
+      addEventListener: (...args) => workerTarget.addEventListener(...args),
+      removeEventListener: (...args) => workerTarget.removeEventListener(...args),
+      postMessage: (message) => {
+        if (!isAlive) {
+          return;
+        }
+
+        clientTarget.dispatchEvent(new MessageEvent('message', { data: message }));
+      },
+    };
+
+    // reason: `no-new-func` is like `eval` except it only executed on global scope and it's easy
+    // to pass in local references. `eval` is very unsafe in production, but in our test environment
+    // we shold be fine.
+    // eslint-disable-next-line no-new-func
+    Function('self', 'require', code)(workerScope, createRelativeRequire(filename));
+  }
+}