[application_deep_links] Unify / improve navigation between apps (ela…

…stic#170228)

## Summary

Attempt at fixing elastic#166893

PR [elastic#168741](elastic#168741) forgot to
update one of the tests to **exclusively** use `navigateToAppLinks`.
Thus, the impacted test had a duplicated navigation logic.

This PR:
* removes that unintended call (this should hopefully fix flakiness).
* simplifies and unifies test logic, improving readability.

Flaky test runner pipeline - 100x 🟢  
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3840

test/plugin_functional/test_suites/core_plugins/application_deep_links.ts

@@ -8,20 +8,24 @@
 
 import url from 'url';
 import expect from '@kbn/expect';
-import { PluginFunctionalProviderContext } from '../../services';
+import type { PluginFunctionalProviderContext } from '../../services';
 
 export default function ({ getService, getPageObjects }: PluginFunctionalProviderContext) {
   const PageObjects = getPageObjects(['common']);
-
   const browser = getService('browser');
   const appsMenu = getService('appsMenu');
   const testSubjects = getService('testSubjects');
   const retry = getService('retry');
   const esArchiver = getService('esArchiver');
   const log = getService('log');
 
-  const loadingScreenNotShown = async () =>
-    expect(await testSubjects.exists('kbnLoadingMessage')).to.be(false);
+  const clickAppLink = async (app: string) => {
+    const appLink = `dlNav${app}`;
+    if (!(await testSubjects.exists(appLink))) {
+      log.debug(`App ${app} not found on side nav`);
+    }
+    await testSubjects.click(appLink);
+  };
 
   const getKibanaUrl = (pathname?: string, search?: string) =>
     url.format({
@@ -42,65 +46,64 @@ export default function ({ getService, getPageObjects }: PluginFunctionalProvide
     });
   };
 
-  const navigateToAppLinks = async (subject: string) => {
-    if (!(await testSubjects.exists(subject))) {
-      log.debug(`side nav in app not in DOM`);
-    }
-    await testSubjects.click(subject);
+  const loadingScreenNotShown = async () =>
+    expect(await testSubjects.exists('kbnLoadingMessage')).to.be(false);
+
+  const checkAppVisible = async (app: string) => {
+    const appContainer = `dlApp${app}`;
+    await testSubjects.existOrFail(appContainer);
   };
 
-  // FLAKY: https://github.com/elastic/kibana/issues/166893
-  describe.skip('application deep links navigation', function describeDeepLinksTests() {
+  describe('application deep links navigation', function describeDeepLinksTests() {
     before(async () => {
       await esArchiver.emptyKibanaIndex();
       await PageObjects.common.navigateToApp('dl');
     });
 
     it('should start on home page', async () => {
-      await testSubjects.existOrFail('dlAppHome');
+      await checkAppVisible('Home');
     });
 
     it('should navigate to page A when navlink is clicked', async () => {
-      await navigateToAppLinks('dlNavPageA');
+      await clickAppLink('PageA');
       await waitForUrlToBe('/app/dl/page-a');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlNavPageA');
+      await checkAppVisible('PageA');
     });
 
     it('should be able to use the back button to navigate back to previous deep link', async () => {
       await browser.goBack();
       await waitForUrlToBe('/app/dl/home');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlNavHome');
+      await checkAppVisible('Home');
     });
 
     it('should navigate to nested page B when navlink is clicked', async () => {
-      await navigateToAppLinks('dlNavDeepPageB');
+      await clickAppLink('DeepPageB');
       await waitForUrlToBe('/app/dl/page-b');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlNavDeepPageB');
+      await checkAppVisible('PageB');
     });
 
     it('should navigate to Home when navlink is clicked inside the defined category group', async () => {
-      await appsMenu.clickLink('DL Home', { category: 'securitySolution' });
-      await navigateToAppLinks('dlAppHome');
+      await clickAppLink('Home');
       await waitForUrlToBe('/app/dl/home');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlAppHome');
+      await checkAppVisible('Home');
     });
 
     it('should navigate to nested page B using navigateToApp path', async () => {
-      await testSubjects.click('dlNavDeepPageB');
+      await clickAppLink('DeepPageB');
       await waitForUrlToBe('/app/dl/page-b');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlNavDeepPageB');
+      await checkAppVisible('PageB');
     });
 
     it('should navigate to nested page A using navigateToApp deepLinkId', async () => {
-      await testSubjects.click('dlNavDeepPageAById');
+      await clickAppLink('DeepPageAById');
       await waitForUrlToBe('/app/dl/page-a');
       await loadingScreenNotShown();
-      await testSubjects.existOrFail('dlNavPageA');
+      await checkAppVisible('PageA');
     });
 
     it('should not display hidden deep links', async () => {