[Canvas] Adds a functional test for expression editor autocomplete (#146943)

## Summary
Fixes https://github.com/elastic/kibana/issues/147887

I added a functional test to check that autocomplete suggestions appear
as you type in the expression editor in Canvas.

[Flaky test runner x
100](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/1658)

### Checklist

Delete any items that are not applicable to this PR.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [ ] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [ ] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)


### Risk Matrix

Delete this section if it is not applicable to this PR.

Before closing this PR, invite QA, stakeholders, and other developers to
identify risks that should be tested prior to the change/feature
release.

When forming the risk matrix, consider some of the following examples
and how they may potentially impact the change:

| Risk | Probability | Severity | Mitigation/Notes |

|---------------------------|-------------|----------|-------------------------|
| Multiple Spaces—unexpected behavior in non-default Kibana Space.
| Low | High | Integration tests will verify that all features are still
supported in non-default Kibana Space and when user switches between
spaces. |
| Multiple nodes—Elasticsearch polling might have race conditions
when multiple Kibana nodes are polling for the same tasks. | High | Low
| Tasks are idempotent, so executing them multiple times will not result
in logical error, but will degrade performance. To test for this case we
add plenty of unit tests around this logic and document manual testing
procedure. |
| Code should gracefully handle cases when feature X or plugin Y are
disabled. | Medium | High | Unit tests will verify that any feature flag
or plugin combination still results in our service operational. |
| [See more potential risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx) |


### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/test/functional/apps/canvas/expression.ts

@@ -10,12 +10,14 @@ import expect from '@kbn/expect';
 import { FtrProviderContext } from '../../ftr_provider_context';
 
 export default function canvasExpressionTest({ getService, getPageObjects }: FtrProviderContext) {
-  const testSubjects = getService('testSubjects');
-  const retry = getService('retry');
+  const archive = 'x-pack/test/functional/fixtures/kbn_archiver/canvas/default';
+  const browser = getService('browser');
+  const find = getService('find');
+  const kibanaServer = getService('kibanaServer');
   const monacoEditor = getService('monacoEditor');
   const PageObjects = getPageObjects(['canvas', 'common']);
-  const kibanaServer = getService('kibanaServer');
-  const archive = 'x-pack/test/functional/fixtures/kbn_archiver/canvas/default';
+  const retry = getService('retry');
+  const testSubjects = getService('testSubjects');
 
   describe('expression editor', function () {
     // there is an issue with FF not properly clicking on workpad elements
@@ -66,8 +68,39 @@ export default function canvasExpressionTest({ getService, getPageObjects }: Ftr
         const editorText = await monacoEditor.getCodeEditorValue(1);
         expect(editorText).to.contain('Orange: Timelion, Server function and this is a test');
       });
+
       // reset the markdown
       await monacoEditor.setCodeEditorValue(oldMd, 0);
     });
+
+    it('does not show autocomplete before typing', async () => {
+      await retry.try(async () => {
+        const elements = await find.allByCssSelector('.monaco-list-rows > .monaco-list-row');
+        expect(elements.length).to.be(0);
+      });
+    });
+
+    it('shows autocomplete when typing', async () => {
+      const originalExpression = await monacoEditor.getCodeEditorValue(1);
+      await monacoEditor.setCodeEditorValue(' ', 1);
+
+      // checks that no suggestions are rendered
+      await retry.try(async () => {
+        const elements = await find.allByCssSelector('.monaco-list-rows > .monaco-list-row');
+        expect(elements.length).to.be(0);
+      });
+
+      await testSubjects.click('canvasExpressionInput');
+      await browser.pressKeys(browser.keys.SPACE);
+
+      // checks that suggestions are rendered after typing
+      await retry.try(async () => {
+        const elements = await find.allByCssSelector('.monaco-list-rows > .monaco-list-row');
+        expect(elements.length).to.be.above(0);
+      });
+
+      // reset expression
+      await monacoEditor.setCodeEditorValue(originalExpression, 1);
+    });
   });
 }