Add tests for preventing duplicate form submit

tests/javascripts/preventDuplicateFormSubmissions.test.js

@@ -0,0 +1,68 @@
+const helpers = require('./support/helpers.js');
+
+beforeAll(() => {
+  jest.useFakeTimers();
+});
+
+afterAll(() => {
+  require('./support/teardown.js');
+});
+
+describe('Prevent duplicate form submissions', () => {
+
+  let form;
+  let button;
+  let formSubmitSpy;
+
+  beforeEach(() => {
+
+    // set up DOM
+    document.body.innerHTML = `
+      <form action="/" method="post">
+        <button class="button" type="submit">Continue</button>
+      </form>`;
+
+    form = document.querySelector('form');
+    button = document.querySelector('button');
+
+    // requires a helper due to JSDOM not implementing the submit method
+    formSubmitSpy = helpers.spyOnFormSubmit(jest, form);
+
+    require('../../app/assets/javascripts/preventDuplicateFormSubmissions.js');
+
+  });
+
+  afterEach(() => {
+
+    document.body.innerHTML = '';
+
+    // we run the previewPane.js script every test
+    // the module cache needs resetting each time for the script to execute
+    jest.resetModules();
+
+    formSubmitSpy.mockClear();
+
+  });
+
+  test("It should prevent any clicks of the 'submit' button after the first one submitting the form", () => {
+
+    helpers.triggerEvent(button, 'click');
+    helpers.triggerEvent(button, 'click');
+
+    expect(formSubmitSpy.mock.calls.length).toEqual(1);
+
+  });
+
+  test("It should allow clicks again after 1.5 minutes", () => {
+
+    helpers.triggerEvent(button, 'click');
+
+    jest.advanceTimersByTime(1500);
+
+    helpers.triggerEvent(button, 'click');
+
+    expect(formSubmitSpy.mock.calls.length).toEqual(2);
+
+  });
+
+});