Add daily test improver workflow for Go test quality automation

[Copilot]

Implements a daily agentic workflow that automatically reviews and improves test files in the Go codebase, focusing on test quality, coverage, and stability.

Workflow Implementation

• .github/workflows/test-improver.md - Agentic workflow with Serena-powered Go analysis
• .github/workflows/test-improver.lock.yml - Compiled GitHub Actions workflow (daily at 08:14 UTC)

Key Capabilities

Intelligent file selection: Uses Serena to rank test files by improvement potential (complexity vs coverage, testing patterns, recent modifications)

Three improvement vectors:

• Idiomatic testing patterns (testify assertions where available, standard library best practices otherwise)
• Coverage gaps (edge cases, error paths, branch coverage)
• Test stability (table-driven tests, proper cleanup, deterministic data)

Smart output: Creates draft PR when improvements made, calls noop safe output when test already excellent. Checks for existing [test-improver] PRs to avoid duplicates.

Tools configured: Serena (Go analysis), GitHub (read-only), edit, bash (test execution, coverage), cache-memory (progress tracking)

Workflow Behavior

Focuses on single test file per run for quality over quantity. Each execution:

1. Discovers all *_test.go files
2. Ranks candidates using Serena complexity analysis
3. Deep analyzes selected file and implementation
4. Implements improvements with verification
5. Creates PR with detailed improvement breakdown or noops

Cache memory prevents immediate repetition across runs.

Original prompt

a daily improver agentic workflow that reviews a single test file and suggest improvements

better idiomatic use of the testify library
increase coverage of the code under test
stabler , cleaner tests
create a pull request if improvements , call noop otherwise

Use serena for go.

Custom agent used: create-agentic-workflow
Design agentic workflows using GitHub Agentic Workflows (gh-aw) extension with interactive guidance on triggers, tools, and security best practices.

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