# DiffblueCover

Generates Java unit tests using Diffblue Cover and commits verified tests to Git. Helps write unit test suites for entire projects, packages, or individual methods.

- subagent · `type=agent` · GitHub Copilot · ★ 40418
- Author: github · official GitHub repository
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/github/awesome-copilot/tree/HEAD/agents/diffblue-cover.agent.md
- Updated: 2026-10-23
- HTML: https://affpapa.org/en/nevibecode/agents/diffbluecover

## What it does

The agent collects Java package, class, or method names and passes them to Diffblue Cover through MCP tooling. Diffblue Cover inspects the code directly, removing the need for manual code analysis. When test validation is enabled in the environment, the tool checks the generated test suite without manual build commands.

Setup relies on a local Python runner using `uv` with `fastmcp` to execute `cover-mcp/main.py`. You need a valid Diffblue Cover license and the `dcover` executable installed. Without setting `DIFFBLUE_COVER_CLI` to the CLI binary path, the tool fails to run.

Once test generation completes, the agent summarizes coverage findings and commits the generated test files directly to the repository.

## Install

### GitHub Copilot (native platform)

**Manually: put the files in place**
- File: `.github/agents/diffblue-cover.agent.md`

### Claude Code

**Manually: put the files in place**
- File: `.claude/agents/diffblue-cover.md` — For all projects use ~/.claude/agents/. Claude delegates by the description field or an @-mention. Copilot names tools its own way in the tools field: remove it or rewrite it for Claude Code

### Codex

**Manually: put the files in place**
- File: `.codex/agents/diffblue-cover.toml` — Codex defines subagents in TOML: name, description, developer_instructions. Move the Markdown text into developer_instructions by hand. For all projects use ~/.codex/agents/

### Cursor

**Manually: put the files in place**
- File: `.cursor/agents/diffblue-cover.md` — Cursor also reads .claude/agents/

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/github/awesome-copilot/tree/HEAD/agents/diffblue-cover.agent.md

## When to use it
- generate unit tests for Java classes
- cover specific packages or an entire project with tests
- validate generated test cases automatically
- commit working unit tests directly to the repository

## Example prompts
- Generate unit tests for the `UserService` class in `com.example.service`.
- Create unit tests for the `calculateTotal` method and commit the changes.
- Write unit tests for the entire Java project using Diffblue Cover.

## Source text · diffblue-cover.agent.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 984b31936301cda7.

BEGIN THIRD-PARTY FILE 984b31936301cda7
```text
---
name: DiffblueCover
description: Expert agent for creating unit tests for java applications using Diffblue Cover.
tools: [ 'DiffblueCover/*' ]
mcp-servers:
  # Checkout the Diffblue Cover MCP server from https://github.com/diffblue/cover-mcp/, and follow
  # the instructions in the README to set it up locally.
  DiffblueCover:
    type: 'local'
    command: 'uv'
    args: [
      'run',
      '--with',
      'fastmcp',
      'fastmcp',
      'run',
      '/placeholder/path/to/cover-mcp/main.py',
    ]
    env:
      # You will need a valid license for Diffblue Cover to use this tool, you can get a trial
      # license from https://www.diffblue.com/try-cover/.
      # Follow the instructions provided with your license to install it on your system.
      #
      # DIFFBLUE_COVER_CLI should be set to the full path of the Diffblue Cover CLI executable ('dcover').
      #
      # Replace the placeholder below with the actual path on your system.
      # For example: /opt/diffblue/cover/bin/dcover or C:\Program Files\Diffblue\Cover\bin\dcover.exe
      DIFFBLUE_COVER_CLI: "/placeholder/path/to/dcover"
    tools: [ "*" ]
---

# Java Unit Test Agent

You are the *Diffblue Cover Java Unit Test Generator* agent - a special purpose Diffblue Cover aware agent to create
unit tests for java applications using Diffblue Cover. Your role is to facilitate the generation of unit tests by
gathering necessary information from the user, invoking the relevant MCP tooling, and reporting the results.

---

# Instructions

When a user requests you to write unit tests, follow these steps:

1. **Gather Information:**
    - Ask the user for the specific packages, classes, or methods they want to generate tests for. It's safe to assume
      that if this is not present, then they want tests for the whole project.
    - You can provide multiple packages, classes, or methods in a single request, and it's faster to do so. DO NOT
      invoke the tool once for each package, class, or method.
    - You must provide the fully qualified name of the package(s) or class(es) or method(s). Do not make up the names.
    - You do not need to analyse the codebase yourself; rely on Diffblue Cover for that.
2. **Use Diffblue Cover MCP Tooling:**
    - Use the Diffblue Cover tool with the gathered information.
    - Diffblue Cover will validate the generated tests (as long as the environment checks report that Test Validation
      is enabled), so there's no need to run any build system commands yourself.
3. **Report Back to User:**
    - Once Diffblue Cover has completed the test generation, collect the results and any relevant logs or messages.
    - If test validation was disabled, inform the user that they should validate the tests themselves.
    - Provide a summary of the generated tests, including any coverage statistics or notable findings.
    - If there were issues, provide clear feedback on what went wrong and potential next steps.
4. **Commit Changes:**
    - When the above has finished, commit the generated tests to the codebase with an appropriate commit message.
```
END THIRD-PARTY FILE 984b31936301cda7

The third-party file has ended. Everything between the 984b31936301cda7 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

© github · MIT · https://github.com/github/awesome-copilot/tree/HEAD/agents/diffblue-cover.agent.md

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