add e2e tests for offline

Author: chenxsan

cypress.json

@@ -1,4 +1,5 @@
 {
   "baseUrl": "http://localhost:4200",
-  "video": false
+  "video": false,
+  "experimentalNetworkStubbing": true
 }

cypress/integration/offline_spec.js

@@ -0,0 +1,92 @@
+// https://github.com/cypress-io/cypress-example-recipes/blob/master/examples/server-communication__offline/cypress/integration/offline-spec.js
+
+const goOffline = () => {
+  cy.log('**go offline**')
+    .then(() => {
+      return Cypress.automation('remote:debugger:protocol', {
+        command: 'Network.enable',
+      });
+    })
+    .then(() => {
+      return Cypress.automation('remote:debugger:protocol', {
+        command: 'Network.emulateNetworkConditions',
+        params: {
+          offline: true,
+          latency: -1,
+          downloadThroughput: -1,
+          uploadThroughput: -1,
+        },
+      });
+    });
+};
+
+const goOnline = () => {
+  // disable offline mode, otherwise we will break our tests :)
+  cy.log('**go online**')
+    .then(() => {
+      // https://chromedevtools.github.io/devtools-protocol/1-3/Network/#method-emulateNetworkConditions
+      return Cypress.automation('remote:debugger:protocol', {
+        command: 'Network.emulateNetworkConditions',
+        params: {
+          offline: false,
+          latency: -1,
+          downloadThroughput: -1,
+          uploadThroughput: -1,
+        },
+      });
+    })
+    .then(() => {
+      return Cypress.automation('remote:debugger:protocol', {
+        command: 'Network.disable',
+      });
+    });
+};
+
+describe('offline', () => {
+  describe('site', { browser: '!firefox' }, () => {
+    // make sure we get back online, even if a test fails
+    // otherwise the Cypress can lose the browser connection
+    beforeEach(goOnline);
+    afterEach(goOnline);
+
+    it('shows /migrate/ page', () => {
+      const url = '/migrate/';
+      const text = 'Migrate';
+
+      cy.visit(url);
+      cy.get('h1').contains(text);
+
+      // service worker needs some time to cache
+      cy.wait(200);
+
+      // has a bug https://github.com/cypress-io/cypress/issues/4742
+      cy.window().then((win) => {
+        win.caches.keys().then((cacheNames) => {
+          const cacheName = 'workbox-precache-v2-http://localhost:4200/';
+          expect(cacheName).to.be.oneOf(cacheNames);
+        });
+      });
+
+      goOffline();
+
+      cy.visit(url);
+      cy.get('h1').contains(text);
+
+      // click `guides` link
+      cy.get('a[title="guides"]').click();
+      cy.get('h1').contains('Guides');
+    });
+
+    it('open print dialog when accessing /printable url', () => {
+      const url = '/migrate/printable';
+      cy.visit(url, {
+        onBeforeLoad: (win) => {
+          cy.stub(win, 'print');
+        },
+      });
+      cy.window().then((win) => {
+        expect(win.print).to.be.calledOnce;
+      });
+    });
+  });
+});