meta: introduce Cypress end-to-end testing (via #4827)

* `test/e2e` -> `test/e2e-selenium`

* add Cypress

* ESLint fixes

* MOAR cypress

* `integration` -> `tests`

* wire Cypress up to a hot e2e server

* linter fixes

* don't run in CI

test/e2e-selenium/scenarios/bugs/4756.js

@@ -0,0 +1,43 @@
+describe("bug #4756: enum initial values", function () {
+  let mainPage
+  beforeEach(function (client, done) {
+    mainPage = client
+      .url("localhost:3230")
+      .page.main()
+
+    client.waitForElementVisible(".download-url-input:not([disabled])", 5000)
+      .pause(2000)
+      .clearValue(".download-url-input")
+      .setValue(".download-url-input", "http://localhost:3230/test-specs/bugs/4756.yaml")
+      .click("button.download-url-button")
+      .pause(1000)
+
+    done()
+  })
+
+  afterEach(function (client, done) {
+    done()
+  })
+
+  it("sets a required initial value based the first enum value", function (client) {
+    client.waitForElementVisible(".opblock-tag-section", 10000)
+      .click("#operations-default-post_zero")
+      .waitForElementVisible(".opblock.is-open", 5000)
+      .click("button.btn.try-out__btn")
+      .click("button.btn.execute")
+      .waitForElementVisible(".request-url", 2000)
+      .assert.containsText(".request-url > pre", "http://www.example.com/test/API/zero?one=0")
+    client.end()
+  })
+
+  it("sets a required initial value based on a default value", function (client) {
+    client.waitForElementVisible(".opblock-tag-section", 10000)
+      .click("#operations-default-post_one")
+      .waitForElementVisible(".opblock.is-open", 5000)
+      .click("button.btn.try-out__btn")
+      .click("button.btn.execute")
+      .waitForElementVisible(".request-url", 2000)
+      .assert.containsText(".request-url > pre", "http://www.example.com/test/API/one?one=1")
+    client.end()
+  })
+})