add test

frontend/util/__tests__/stop_ie_test.ts

@@ -0,0 +1,50 @@
+import { stopIE } from "../stop_ie";
+
+describe("stopIE()", () => {
+  beforeEach(() => {
+    window.location.assign = jest.fn();
+    window.alert = jest.fn();
+    window.hasOwnProperty = () => true;
+    Array.prototype.hasOwnProperty = () => true;
+    Object.defineProperty(Object, "entries", {
+      value: true, configurable: true
+    });
+  });
+
+  const expectToHaveBeenStopped = () => {
+    expect(window.alert).toHaveBeenCalledWith(
+      "This app only works with modern browsers.");
+    expect(window.location.assign).toHaveBeenCalledWith(
+      "https://www.google.com/chrome/");
+  };
+
+  it("doesn't block when requirements are met", () => {
+    stopIE();
+    expect(window.alert).not.toHaveBeenCalled();
+    expect(window.location.assign).not.toHaveBeenCalled();
+  });
+
+  it("blocks when requirements not met", () => {
+    Object.defineProperty(Object, "entries", { value: undefined });
+    stopIE();
+    expectToHaveBeenStopped();
+  });
+
+  it("blocks when requirements not met: window", () => {
+    window.hasOwnProperty = () => false;
+    stopIE();
+    expectToHaveBeenStopped();
+  });
+
+  it("blocks when requirements not met: array", () => {
+    Array.prototype.hasOwnProperty = () => false;
+    stopIE();
+    expectToHaveBeenStopped();
+  });
+
+  it("blocks when requirements not met: error", () => {
+    Array.prototype.hasOwnProperty = () => { throw new Error(); };
+    stopIE();
+    expectToHaveBeenStopped();
+  });
+});

frontend/util/stop_ie.ts

@@ -3,7 +3,7 @@ function flunk() {
   // IE Cannot handle it.
   const READ_THE_COMMENT_ABOVE = "This app only works with modern browsers.";
   alert(READ_THE_COMMENT_ABOVE);
-  window.location.href = "https://www.google.com/chrome/";
+  window.location.assign("https://www.google.com/chrome/");
 }
 
 const REQUIRED_GLOBALS = [