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/4196.js

@@ -0,0 +1,44 @@
+describe("bug #4196: HTTP basic auth credential retention", function () {
+    let mainPage
+    beforeEach(function (client, done) {
+        mainPage = client
+            .url("localhost:3230")
+            .page.main()
+
+        client.waitForElementVisible(".download-url-input:not([disabled])", 5000)
+            .pause(80)
+            .clearValue(".download-url-input")
+            .setValue(".download-url-input", "http://localhost:3230/test-specs/bugs/4196.yaml")
+            .click("button.download-url-button")
+            .pause(1000)
+
+        done()
+    })
+    afterEach(function (client, done) {
+        done()
+    })
+    it("should display the most recent auth data across modal close/opens", function (client) {
+        client.waitForElementVisible(".opblock-tag-section", 10000)
+            .click("button.btn.authorize") // Open modal
+            .waitForElementVisible("section>input", 5000)
+            .setValue("section>input", "aaa") // Set user
+            .waitForElementVisible(`section>input[type="password"]`, 5000)
+            .setValue(`section>input[type="password"]`, "aaa") // Set password
+            .click(".auth-btn-wrapper button:nth-child(1)") // Click Authorize
+            .assert.containsText("div.wrapper:nth-child(4)>code", "aaa")
+            .click(".auth-btn-wrapper button:nth-child(2)") // Close modal
+            .pause(50)
+            .click("button.btn.authorize") // Open modal
+            .pause(50)
+            .click(".auth-btn-wrapper button:nth-child(1)") // Logout
+            .waitForElementVisible("section>input", 5000)
+            .setValue("section>input", "bbb") // Set user
+            .waitForElementVisible(`section>input[type="password"]`, 5000)
+            .setValue(`section>input[type="password"]`, "bbb") // Set password
+            .click(".auth-btn-wrapper button:nth-child(1)") // Click Authorize
+            .pause(5000)
+            .assert.containsText("div.wrapper:nth-child(4)>code", "bbb")
+
+        client.end()
+    })
+})