--- title: "Diffblue Cover Java Unit Test Agent: review, role & definition · Undominated.ai" canonical: https://undominated.ai/agents/github-diffblue-cover/ description: "Collects the Java packages, classes or methods to cover, runs Diffblue Cover through its MCP server, reports the result and commits the tests." --- # Diffblue Cover Java Unit Test Agent: review, role & definition · Undominated.ai > Collects the Java packages, classes or methods to cover, runs Diffblue Cover through its MCP server, reports the result and commits the tests. [← Explore all agents](/agents/) TESTING AND REVIEW / GitHub partners # Diffblue Cover Java Unit Test Agent Collects the Java packages, classes or methods to cover, runs Diffblue Cover through its MCP server, reports the result and commits the tests. [Use this definition ↓](#setup)[Original source ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/agents/diffblue-cover.agent.md) SOURCE REVIEW Reviewed 2026-10-13 Evidence 5 linked sources Publisher GitHub partners Licence [MIT ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/LICENSE) Revision 156736fb63e9 [Read what was—and wasn’t—checked ↓](#review) “Expert agent for creating unit tests for java applications using Diffblue Cover.” [GitHub partners · upstream description ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/agents/diffblue-cover.agent.md) Our analysis follows below. 01 / THE REASONING ## Why this made the selection. - Tools are limited to the DiffblueCover MCP server. Test generation and validation are delegated to Diffblue Cover rather than written by the model. - It must use fully qualified names and not make them up, sends several targets in one call, and tells the user to validate the tests when Cover's test validation is disabled. ### A good fit for - Generating unit tests for Java code with an existing Diffblue Cover licence - Adding unit tests for several named Java packages, classes or methods in one request ### Weigh up before choosing - Step 4 commits the generated tests with no review step in between. Review the diff first. - Step 4 asks for a commit, but no git or shell tool is declared; whether the commit happens depends on the host and the Cover tools. - Requires a Diffblue Cover licence, the dcover CLI and a local clone of diffblue/cover-mcp. The paths in the mcp-servers block are placeholders. 02 / THE REVIEW RECORD ## What we actually inspected. Source review has boundaries. A clear record is more useful than a “safe” badge. ### Material inspected - agents/diffblue-cover.agent.md - plugins/partners/plugin.json and README.md - LICENSE ### Our findings - Listed in plugins/partners/plugin.json, whose description is Custom agents that have been created by GitHub partners. The commit history was not used to attribute authorship. - If no target is given it assumes the whole project. ### Not established by this review - The agent and the Cover MCP server were not run. - diffblue/cover-mcp was not opened. The review applies to the material and revision named here. A newer upstream release can change its behavior. 03 / PUT IT TO WORK ## Use the role in your project. [Upstream setup instructions ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/plugins/partners/README.md) DOCUMENTED COMMAND copilot plugin install partners@awesome-copilot Copy command ↗ Copying does not execute this command. It may retrieve a newer version than the reviewed source. - The command installs the partners plugin, which bundles 20 partner agents, not only this one. - For this agent alone, download the unchanged diffblue-cover.agent.md with its LICENSE.txt and place a reviewed copy in the workspace .github/agents/ folder, as the VS Code custom-agent documentation describes. - Clone diffblue/cover-mcp and replace both placeholder paths in the mcp-servers block, as the file's comments say. ### Before you start - GitHub Copilot with custom agents - A Diffblue Cover licence and the dcover CLI - uv, to run the local MCP server - A Java project ### Compatibility GitHub Copilot CLI (partners plugin) · GitHub Copilot custom agents (the mcp-servers block applies to the github-copilot target) ### Local Diffblue Cover MCP server only - Declared tools: DiffblueCover/*. - The local MCP server runs uv run --with fastmcp fastmcp run on cover-mcp/main.py, with DIFFBLUE_COVER_CLI pointing at dcover. ### Cost model MIT-licensed definition. Diffblue Cover needs its own licence; the file links a trial. Copilot and model usage have their own charges. THE COMPLETE REVIEWED DEFINITION ## Read it before you reuse it. Original source bytes, with attribution. Review the host-specific setup notes above. Copy definition ↗ [Download definition + licence ↗](/resources/agents/github-diffblue-cover/bundle.zip)[Raw Markdown ↗](/resources/agents/github-diffblue-cover/definition.md) --- 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. The download contains diffblue-cover.agent.md . Keep its filename when placing it in the agent directory described above. By **GitHub partners**. [Exact upstream source ↗](https://raw.githubusercontent.com/github/awesome-copilot/156736fb63e965b2f547a1460f3b5972c46e6b24/agents/diffblue-cover.agent.md) · [Licence](/resources/agents/github-diffblue-cover/LICENSE.txt) · [Attribution](/resources/agents/github-diffblue-cover/ATTRIBUTION.txt) SHA-256 52cfa54cae231f158595989f0483461770150bfe5e4d9c31c45ab3ead2f6e389 Read the applicable licence MIT License Copyright GitHub, Inc. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 04 / FOLLOW THE EVIDENCE ## The source trail. Our notes are separate from the original resource. Check upstream before adopting a new version. - [Agent definition ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/agents/diffblue-cover.agent.md) Checked 2026-10-13 https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/agents/diffblue-cover.agent.md Supports: summary, upstreamDescription, whySelected, limitations, access, review - [Partners plugin manifest ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/plugins/partners/plugin.json) Checked 2026-10-13 https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/plugins/partners/plugin.json Supports: publisher - [Partners plugin README: install line ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/plugins/partners/README.md) Checked 2026-10-13 https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/plugins/partners/README.md Supports: install - [Repository licence (MIT) ↗](https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/LICENSE) Checked 2026-10-13 https://github.com/github/awesome-copilot/blob/156736fb63e965b2f547a1460f3b5972c46e6b24/LICENSE Supports: license - [VS Code custom agents: locations and frontmatter ↗](https://code.visualstudio.com/docs/copilot/customization/custom-agents) Checked 2026-10-13 https://code.visualstudio.com/docs/copilot/customization/custom-agents Supports: install, compatibility KEEP COMPARING ## Other approaches to consider. Related by category or shared topics. These are alternatives to inspect, not a measured quality order. [### Java Reviewer ↗ Detects Spring Boot versus Quarkus from the build file first and runs the framework build check, then reviews Java changes against framework-specific rules spanning JPA, Panache, MongoDB, security and concurrency.](/agents/ecc-java-reviewer/)[### Playwright Test Explorer ↗ Explores a working interface through Playwright before generating and running TypeScript tests for its observed user flows.](/agents/github-playwright-tester/)[### AWS provider maintainer review ↗ A short review persona for AWS provider changes. It says not to open pull requests.](/agents/hashicorp-aws-provider-maintainer/) [AI Tools ↗](/tools/)[Skills ↗](/skills/)[Agents ↗](/agents/)[MCP Servers ↗](/mcp-servers/)[Workflows ↗](/workflows/) ## Continue your investigation - [Find reusable instructions](/skills/) - [Inspect connections](/mcp-servers/) - [Build a toolkit](/tools/) - [Choose the model](/compare/)