[Tests] Normalize subtree test names and reuse message constant

[mrz1836]

What Changed

• Added a shared constant for the repeated "expected size to be 4" assertion message in subtree_test.go.
• Renamed subtree test functions to comply with Go's testing naming conventions by removing underscores and ensuring uniqueness.

Why It Was Necessary

• Deduplicating the assertion message resolves the goconst warning around repeated literals and simplifies future updates.
• Renaming the affected tests eliminates lint failures triggered by the repository's naming rules while avoiding duplicate declarations.

Testing Performed

• go test ./...
• golangci-lint run (fails in this environment because the configured linters arangolint, embeddedstructfieldcheck, and wsl_v5 are not recognized by the installed golangci-lint build)

Impact / Risk

• No functional code changes; test-only updates.
• Low risk of regressions since production code is untouched.
• Assigning reviewer: @mrz1836

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https://chatgpt.com/codex/tasks/task_e_68e8488070648321bc47c770e6794d68

[Copilot]

Pull Request Overview

This PR improves test code maintainability by normalizing test function names and eliminating code duplication in subtree tests.

• Added a shared constant expectedSizeFourMessage to replace repeated "expected size to be 4" assertion messages
• Renamed test functions to follow Go naming conventions by removing underscores
• Replaced all hardcoded error message strings with the new constant

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[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[sonarqubecloud]

Quality Gate failed

Failed conditions
34.5% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud