[Security Solution] Audit existing test coverage for the Alerts area

[banderror]

Epic: #153633

Summary

• Create a list of all features of the Detection Engine that are owned by the Alerts area.
• Review existing test coverage and see how it matches the list of features.
• For each feature:
  • evaluate the coverage at each level (E2E, integration, unit; e.g. full, some, none)
  • determine gaps (e.g. this use case is covered, but that one is not; integration tests exist but e2e tests are missing)
  • check if there are any Cypress tests we can drop because the behavior is already covered at a different level (integration or unit)
  • check if there are any Cypress tests that can be covered at a different level (integration or unit)
  • check for any unnecessary/redundant actions or assertions in Cypress tests -- these should be either removed or extracted into other tests

Document and share the results of the audit with the other 2 area teams.

Based on the results, create as many GitHub issues as needed, titled [Security Solution] Increase test coverage for <Feature X>. In general, the goals of each of these issues should be:

• Write a test plan for <Feature X>.
• Write missing tests.
• Fix and improve existing tests: make them less flaky and brittle (reduce false negatives), more isolated from each other, etc.

Feel free to add any other goals specific to the feature.

Finally, please add all these issues to the epic, to the task list called Increase test coverage for the Alerts area.

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[banderror]

Replaced by #153638