setup mock browser object

__mocks__/webextension-polyfill-ts/index.ts

@@ -0,0 +1,19 @@
+class BrowserMock {
+  runtime = {
+    getBackgroundPage() {
+      return 'https://background-page.html';
+    },
+    getManifest() {
+      return {
+        version: 'test-version',
+      };
+    },
+    openOptionsPage() {
+      return 'https://options-page.html';
+    },
+  };
+}
+
+export const browser = new BrowserMock();
+
+export default { browser };