Filter for APM property file in APM tests

[mamazzol]

Inside the tempDir created to store APM properties, there are possibly other files/folders.
Tightening the filter in the test to reduce flakiness.
Closes: #144338

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[prdoyle]

Optional simplification

[prdoyle]

This regex seems a bit obfuscated. If I understand, it corresponds roughly to this glob:

.elstcapm.*.tmp

(Except the regex allows for slashes where a glob * does not.)

Could we use the following? It seems a little more readable than an escaped regex.

files.filter(p -> p.startsWith(".elstcapm") && p.endsWith(".tmp"))

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository YAML (base), Organization UI (inherited)

Review profile: CHILL

Plan: Pro

Run ID: 242ed8f8-bff7-44f0-899b-8117b62e0b36

📥 Commits

Reviewing files that changed from the base of the PR and between 40dc1ba and 575c9e6.

📒 Files selected for processing (1)

• distribution/tools/server-cli/src/test/java/org/elasticsearch/server/cli/APMJvmOptionsTests.java

---

📝 Walkthrough

Walkthrough

The change modifies the file selection logic in APMJvmOptionsTests to use a more specific filtering criterion. Instead of selecting any arbitrary file from a temporary directory, the code now filters files to match those with names starting with ".elstcapm" and ending with ".tmp". If no matching files are found, it raises the same assertion error as before. This targeted filtering ensures the test selects the correct configuration file instead of potentially picking a directory.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR directly addresses issue #144338 by filtering the temp directory to select only APM property files (names starting with '.elstcapm' and ending with '.tmp'), preventing the test from attempting to read directories as properties files and resolving the IOException.
Out of Scope Changes check	✅ Passed	All changes are scoped to APMJvmOptionsTests.java and directly address the identified test failure; no extraneous modifications are present.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

• 🛠️ Update Documentation: Commit on current branch
• 🛠️ Update Documentation: Create PR

📝 Coding Plan

• Generate coding plan for human review comments

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Tip

CodeRabbit can use TruffleHog to scan for secrets in your code with verification capabilities.

Add a TruffleHog config file (e.g. trufflehog-config.yml, trufflehog.yml) to your project to customize detectors and scanning behavior. The tool runs only when a config file is present.