test: add coverage for terminal yes/no prompt parsing

[github-actions]

Summary

• Added libbeat/common/terminal/terminal_test.go.
• Added coverage for ReadInput() newline trimming.
• Added coverage for PromptYesNo() behavior for default answers, mixed-case yes, and whitespace-padded no.

User scenarios covered

• When a user runs keystore commands that ask for confirmation (for example overwrite/create prompts in libbeat/cmd/keystore.go), pressing Enter now has explicit tests proving default handling.
• When a user types yes in different capitalization, tests verify the command treats it as confirmation.
• When a user types no with accidental surrounding spaces, tests verify the command still rejects as expected.

Why this matters

• These tests protect interactive CLI confirmation behavior used by keystore workflows.
• Regressions in answer parsing (default, case, trimming) would now fail tests instead of surfacing to users at runtime.

Tests run

• go test ./libbeat/common/terminal -count=5 (pass)
• go test ./libbeat/common/terminal -count=1 (pass)

Removed or merged tests

• None.

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What is this? | From workflow: Test Improver

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[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @github-actions[bot]? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 8dddfb58-8c3b-41ec-be3d-23f3cac6aa60

📥 Commits

Reviewing files that changed from the base of the PR and between d09baaf and 2c2cb48.

📒 Files selected for processing (1)

• libbeat/common/terminal/terminal_test.go

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📝 Walkthrough

Walkthrough

A new test file was added to libbeat/common/terminal/terminal_test.go containing unit tests for terminal input functions. The file includes a helper function that manages stdin redirection for testing purposes. Two test functions were introduced: TestReadInput validates the ReadInput() function's ability to read and return stdin input, and TestPromptYesNo uses table-driven test cases to verify PromptYesNo() behavior across various input scenarios including yes, no, default responses, mixed-case input, and whitespace handling.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch test-improve-terminal-prompt-25b5ec70d99a4fcb

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

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

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mauri870]

Tested with stress, tests are stable.