[TG-23867] Productize Cover MCP Server #1

pcrane · 2025-10-29T12:02:02Z

JIRA Link (if applicable)

Description

Productionise the Cover MCP server by migrating from custom implementation to FastMCP framework and adding
production-ready infrastructure:

Architecture: Migrate to FastMCP with modular covermcp package (server.py, executor.py)
Testing: Add comprehensive test suite achieving 98% coverage (19 tests)
Tooling: Implement uv package manager with locked dependencies
CI/CD: Add GitHub Actions workflow with security scanning, linting, formatting, and testing
Governance: Add CODEOWNERS requiring review from @pcrane and @peterschrammel
Documentation: Update README.md with FastMCP installation instructions

Decision References (if applicable)

Third-party software additions:

FastMCP (v2.12.5+): MCP server framework - https://gofastmcp.com/
uv: Modern Python package manager - https://docs.astral.sh/uv/
Ruff (v0.14.2+): Python linter/formatter - https://docs.astral.sh/ruff/

QA Notes (How can this be tested?)

Local testing:

# Clone and setup
uv sync --all-extras

# Run quality checks (all should pass)
uv run ruff check
uv run ruff format --check
uv run pytest -v
uv run coverage report  # Should show 98%

# Test MCP server locally
uv run fastmcp dev  # Opens MCP Inspector

# Test installation
uv run fastmcp install claude-code

Integration testing:

Install in LLM client (Claude Code/Desktop recommended)
Verify create tool appears in MCP tools list
Test with Java project: invoke tool to generate tests

CI/CD verification:

GitHub Actions workflow runs automatically on PR
All checks must pass (linting, formatting, security, tests)

Are there any changes to user messages or documentation that need review by Technical Writing Team?

Yes - README.md was significantly rewritten with:

New installation instructions using FastMCP
Environment variable documentation
Development workflow guide
Removal of legacy manual configuration instructions

Is there a chance that this PR will break unattended customer installations?

Yes - Breaking changes:

Installation method changed: Old manual MCP configuration no longer works. Users must:

Uninstall old configuration
Reinstall using: uv run fastmcp install main.py

Legacy server removed: src/mcp_diffblue_server.py deleted. Any direct references will break.
Dependency changes: Now requires uv package manager and FastMCP framework.

Set up project configuration using uv as the package manager. Define dependencies (fastmcp) and dev dependencies (pytest, coverage, ruff). Configure Ruff linter with Google-style docstrings. Target Python 3.14.

Copilot

Pull Request Overview

This PR productionizes the Cover MCP server by migrating from a custom implementation to the FastMCP framework, adding comprehensive testing infrastructure, and implementing modern Python tooling with locked dependencies.

Key changes:

Migration to FastMCP framework with modular covermcp package architecture
Addition of comprehensive test suite achieving 98% coverage across 19 tests
Implementation of GitHub Actions CI/CD pipeline with security scanning, linting, and testing

Reviewed Changes

Copilot reviewed 14 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
`test/test_server.py`	Tests for server module covering tool invocation, environment variable handling, and error scenarios
`test/test_executor.py`	Tests for executor module covering process execution, timeout handling, and output streaming
`test/__init__.py`	Test package initialization with copyright header
`src/mcp_diffblue_server.py`	Removal of legacy custom MCP server implementation
`pyproject.toml`	Project configuration with FastMCP dependencies and Ruff tooling setup
`main.py`	New entry point for running the FastMCP server
`fastmcp.json`	FastMCP configuration specifying server entry point
`covermcp/server.py`	New FastMCP-based server implementation with create tool
`covermcp/executor.py`	Process execution module with streaming output and timeout handling
`covermcp/__init__.py`	Package initialization exporting server components
`README.md`	Updated documentation with FastMCP installation instructions and development workflow
`CODEOWNERS`	Code ownership assignment to pcrane and peterschrammel
`.python-version`	Python version specification (3.14)
`.github/workflows/PullRequest.yml`	CI/CD workflow for quality checks and testing

Comments suppressed due to low confidence (1)

test/test_executor.py:1

Missing docstring for public function cleanup_process. Add a docstring explaining that this function kills a process and waits for it to terminate with a timeout.

#  Copyright 2025 Diffblue

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Copilot

Pull Request Overview

Copilot reviewed 14 out of 16 changed files in this pull request and generated 2 comments.

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.github/workflows/Build.yml

.github/workflows/PullRequest.yml

roxspring

LGTM in principle but I can't really comment on python specific idioms and best practice

Replace custom MCP server with FastMCP-based implementation. Create covermcp package with modular architecture: - server.py: FastMCP tool definitions and dcover executable discovery - executor.py: Process execution with real-time streaming and timeout handling Implement 'create' tool with support for entry points, custom paths, and environment variable configuration (DIFFBLUE_COVER_CLI, DIFFBLUE_COVER_OPTIONS).

Create main.py to run the FastMCP server, allowing LLMs to interact with the Diffblue Cover tools defined in covermcp.server.

Implement unit tests for server and executor modules using pytest. Configure coverage reporting to track test coverage.

Rewrite README to focus on FastMCP installation and usage. Add sections for: - Installation via fastmcp install for multiple LLM clients - Environment variable configuration - Development workflow with MCP Inspector - Testing and linting instructions Remove outdated manual MCP configuration instructions.

Delete old custom MCP server implementation (src/mcp_diffblue_server.py). Fix typo in .gitignore (*.py[codz] -> *.py[cod]). Add PyCharm IDE directory (.idea) to .gitignore.

Add uv.lock to ensure reproducible builds with pinned dependency versions.

Exclude .claude/ directory from version control as it contains local IDE configuration and settings specific to individual developer environments.

@pcrane

Define code ownership for automated review assignment. All changes require review from @pcrane and @peterschrammel.

Implement automated testing and quality checks for pull requests and main branch pushes. The pipeline includes: - Dependency installation with uv - Security vulnerability scanning with uv-secure - Code linting with ruff - Code formatting verification with ruff - Test execution with pytest - Coverage reporting All checks must pass before code can be merged, ensuring consistent quality standards.

Add regex pattern to remove ANSI escape sequences from dcover output lines. This ensures clean, readable output in MCP clients that don't properly handle terminal control codes. Changes: - Import re module - Define ANSI_ESCAPE pattern for matching escape sequences - Strip escape codes before yielding output lines

Implement 'write tests' prompt that provides LLMs with contextual guidance for writing Java unit tests. The prompt establishes the assistant's role as a skilled test writer, improving the quality of test generation suggestions. This prompt can be invoked by LLM clients to get specialized instructions before using the create tool.

Expose comprehensive dcover configuration documentation through an MCP resource (data://config). This allows LLM clients to query available dcover options and their descriptions, enabling intelligent tool usage and better test generation configurations. The resource includes 50+ dcover CLI options covering: - Test framework selection - Mocking strategies (Mockito, Spring) - Coverage options - Build system preferences - Output customization - Security and sandbox settings Marked as read-only and idempotent for efficient caching.

Enable LLMs to pass arbitrary dcover CLI options through a new 'args' parameter in the create tool. This provides maximum flexibility for advanced test generation configurations without requiring predefined parameters for every possible option. Changes: - Add 'args' parameter to create() function signature - Document parameter in function docstring - Add logic to append args to command before environment options - Log args when provided for debugging Order of precedence for options: 1. Base command with --batch 2. LLM-provided args (new) 3. Environment variable DIFFBLUE_COVER_OPTIONS 4. Entry points This allows LLMs to leverage the comprehensive dcover options documented in the MCP resource while maintaining backward compatibility.

yumibagge

QA review 🆗

Happy path confirmed - but will explorer a bit more

https://diffblue.atlassian.net/browse/TG-23925?focusedCommentId=72102

Initialize Python project with uv and FastMCP

043e0d5

Set up project configuration using uv as the package manager. Define dependencies (fastmcp) and dev dependencies (pytest, coverage, ruff). Configure Ruff linter with Google-style docstrings. Target Python 3.14.

pcrane requested review from Copilot and peterschrammel October 29, 2025 12:02

pcrane self-assigned this Oct 29, 2025

Copilot AI reviewed Oct 29, 2025

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pcrane requested review from a team and JohnLBergqvist October 29, 2025 12:02

pcrane force-pushed the pcrane/feature/productionise-cover-mcp-server branch from 7a1f008 to a7e2c4a Compare October 29, 2025 12:13

pcrane requested a review from Copilot October 29, 2025 12:13

Copilot AI reviewed Oct 29, 2025

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roxspring approved these changes Oct 29, 2025

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pcrane force-pushed the pcrane/feature/productionise-cover-mcp-server branch 2 times, most recently from 32259d0 to 7c86c4c Compare October 29, 2025 12:36

pcrane added 2 commits October 31, 2025 14:29

Add MCP server entry point

f20ac35

Create main.py to run the FastMCP server, allowing LLMs to interact with the Diffblue Cover tools defined in covermcp.server.

pcrane force-pushed the pcrane/feature/productionise-cover-mcp-server branch from 7c86c4c to d2e3a66 Compare October 31, 2025 14:30

peterschrammel approved these changes Oct 31, 2025

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peterschrammel changed the title ~~[TG-23867] Productionise Cover MCP Server~~ [TG-23867] Productize Cover MCP Server Oct 31, 2025

pcrane force-pushed the pcrane/feature/productionise-cover-mcp-server branch 8 times, most recently from 433cde0 to 7c2981c Compare November 4, 2025 12:21

pcrane added 4 commits November 4, 2025 12:24

Add comprehensive test suite

1c1aaf4

Implement unit tests for server and executor modules using pytest. Configure coverage reporting to track test coverage.

Remove legacy MCP server and update .gitignore

039f970

Delete old custom MCP server implementation (src/mcp_diffblue_server.py). Fix typo in .gitignore (*.py[codz] -> *.py[cod]). Add PyCharm IDE directory (.idea) to .gitignore.

Lock project dependencies

6894e45

Add uv.lock to ensure reproducible builds with pinned dependency versions.

pcrane added 7 commits November 4, 2025 12:24

Add Claude Code directory to .gitignore

37de626

Exclude .claude/ directory from version control as it contains local IDE configuration and settings specific to individual developer environments.

Add CODEOWNERS file

f8c36b1

Define code ownership for automated review assignment. All changes require review from @pcrane and @peterschrammel.

pcrane force-pushed the pcrane/feature/productionise-cover-mcp-server branch from 7c2981c to fd679e9 Compare November 4, 2025 12:24

JohnLBergqvist approved these changes Nov 4, 2025

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yumibagge self-requested a review November 5, 2025 16:22

yumibagge approved these changes Nov 5, 2025

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pcrane merged commit 155f3d1 into main Nov 5, 2025
1 check passed

pcrane deleted the pcrane/feature/productionise-cover-mcp-server branch November 6, 2025 11:49

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pcrane commented Oct 29, 2025 •

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JIRA Link (if applicable)

Description

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QA Notes (How can this be tested?)

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Pull Request Overview

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pcrane commented Oct 29, 2025 •

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