DiffblueCover
Expert agent for creating unit tests for java applications using Diffblue Cover.
- Type
- Subagent
- Repository
- github/awesome-copilot
- GitHub stars
- 39.4k
- License
- MIT
- Repo last updated
- Sep 27, 2026
- Source file
- agents/diffblue-cover.agent.md
What DiffblueCover is
DiffblueCover is a subagent published in the github/awesome-copilot repository on GitHub, which has about 39.4k stars. The repository describes itself as: “Community-contributed instructions, agents, skills, and configurations to help you make the most of GitHub Copilot.”
A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.
Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to DiffblueCover and get back a compact result.
It is set up to use these tools: 'DiffblueCover/*' . Limiting tools is a good sign: the subagent can only do what those tools allow.
How to install DiffblueCover
Claude Code
- Download diffblue-cover.agent.md from the repository.
- Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
- Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Claude Cowork
- Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
- Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.
Inside the source file
An excerpt from agents/diffblue-cover.agent.md, shared under the repository's MIT license. Read the full file on GitHub.
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:
- 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.
- 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.
- 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.
- Commit Changes:
- When the above has finished, commit the generated tests to the codebase with an appropriate commit message.
Before you install
- Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
- Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
- Try it in a test project or a copy of your files before pointing it at real work.
- Pin the version you tested, and review changes before updating.
- Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.
FAQ
What is DiffblueCover?
DiffblueCover is a subagent for Claude Code and Claude Cowork from the github/awesome-copilot repository on GitHub. Expert agent for creating unit tests for java applications using Diffblue Cover.
How do I install DiffblueCover in Claude Code?
Download diffblue-cover.agent.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Can I use DiffblueCover in Claude Cowork?
Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
Is DiffblueCover safe to install?
It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.
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