Add initial e2e testing with cypress

Add e2e tests with cypress using `vue add e2e-cypress`.

Vue CLI does not support creating typescript tests at this moment
(vuejs/vue-cli#1350).

tests/e2e/plugins/index.js

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+/* eslint-disable arrow-body-style */
+// https://docs.cypress.io/guides/guides/plugins-guide.html
+
+// if you need a custom webpack configuration you can uncomment the following import
+// and then use the `file:preprocessor` event
+// as explained in the cypress docs
+// https://docs.cypress.io/api/plugins/preprocessors-api.html#Examples
+
+// /* eslint-disable import/no-extraneous-dependencies, global-require */
+// const webpack = require('@cypress/webpack-preprocessor')
+
+module.exports = (on, config) => {
+  // on('file:preprocessor', webpack({
+  //  webpackOptions: require('@vue/cli-service/webpack.config'),
+  //  watchOptions: {}
+  // }))
+
+  return Object.assign({}, config, {
+    fixturesFolder: 'tests/e2e/fixtures',
+    integrationFolder: 'tests/e2e/specs',
+    screenshotsFolder: 'tests/e2e/screenshots',
+    videosFolder: 'tests/e2e/videos',
+    supportFile: 'tests/e2e/support/index.js'
+  })
+}

tests/e2e/specs/initialization.spec.js

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+describe('application is initialized as expected', () => {
+  it('loads title as expected', () => {
+    // act
+    cy.visit('/');
+    // assert
+    cy.contains('h1', 'privacy.sexy')
+  });
+  it('there are no console.error output', () => {
+    // act
+    // https://docs.cypress.io/faq/questions/using-cypress-faq#How-do-I-spy-on-console-log
+    cy.visit('/', {
+      onBeforeLoad(win) {
+        cy.stub(win.console, 'error').as('consoleError')
+      }
+    });
+    // assert
+    cy.get('@consoleError').should('have.not.been.called');
+  });
+  it('there are no console.warn output', () => {
+    // act
+    cy.visit('/', {
+      onBeforeLoad(win) {
+        cy.stub(win.console, 'warn').as('consoleWarn')
+      }
+    });
+    // assert
+    cy.get('@consoleWarn').should('have.not.been.called');
+  });
+  it('there are no console.log output', () => {
+    // act
+    cy.visit('/', {
+      onBeforeLoad(win) {
+        cy.stub(win.console, 'log').as('consoleLog')
+      }
+    });
+    // assert
+    cy.get('@consoleLog').should('have.not.been.called');
+  });
+});

tests/e2e/support/commands.js

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+// ***********************************************
+// This example commands.js shows you how to
+// create various custom commands and overwrite
+// existing commands.
+//
+// For more comprehensive examples of custom
+// commands please read more here:
+// https://on.cypress.io/custom-commands
+// ***********************************************
+//
+//
+// -- This is a parent command --
+// Cypress.Commands.add("login", (email, password) => { ... })
+//
+//
+// -- This is a child command --
+// Cypress.Commands.add("drag", { prevSubject: 'element'}, (subject, options) => { ... })
+//
+//
+// -- This is a dual command --
+// Cypress.Commands.add("dismiss", { prevSubject: 'optional'}, (subject, options) => { ... })
+//
+//
+// -- This is will overwrite an existing command --
+// Cypress.Commands.overwrite("visit", (originalFn, url, options) => { ... })

tests/e2e/support/index.js

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+// ***********************************************************
+// This example support/index.js is processed and
+// loaded automatically before your test files.
+//
+// This is a great place to put global configuration and
+// behavior that modifies Cypress.
+//
+// You can change the location of this file or turn off
+// automatically serving support files with the
+// 'supportFile' configuration option.
+//
+// You can read more here:
+// https://on.cypress.io/configuration
+// ***********************************************************
+
+// Import commands.js using ES2015 syntax:
+import './commands'
+
+// Alternatively you can use CommonJS syntax:
+// require('./commands')