How three Java Champions use GitHub Copilot for migration, testing and app building

Three experienced Java developers describe how they use GitHub Copilot in IDEs and agent workflows for feature work, a slide-deck migration, UI test reproduction and small apps. They stress planning, verification gates and reusable skills while keeping ownership of the result.

The problem

Quick code generation does not solve the harder parts of engineering: supplying context, checking results, keeping code maintainable and staying accountable for what ships. The developers had tedious or postponed work, such as migrating hundreds of slides, building a performance-history web app and reproducing platform-specific UI bugs, that would normally take days or weeks by hand.

How they did it

1. Choose the interface by the feedback loop needed: IntelliJ IDEA or VS Code for close visual review, or the terminal or GitHub coding agent for delegated, larger tasks.
2. Avoid one-shot prompts: ask the agent to interview you first, then agree on a plan with visible assumptions and an architecture fit.
3. Define task-specific verification gates, such as screenshots, visual diffs, PDF comparison, passing tests and no leftover TODOs, so the agent must show evidence of completion.
4. Write reusable Agent Skills, for example one that mimics your writing voice or a maintainer-audit skill, and update them after each lesson learned.
5. Wrap Checkstyle, PMD and Spring Modulith checks in a quality harness run from hooks so the agent loops until no findings remain.
6. Match the model to the task: a large-context, high-reasoning model for deep work and lighter models for reports, release notes or doc checks.

Results

• As reported by the GitHub Blog (developer quotes): Vlad Mihalcea built an Optimizer event-history web app in two days, a task he expected to take weeks.
• As reported by the GitHub Blog: Patrick Baumgartner migrated around 900 teaching slides across 15 presentations from Reveal.js to Marp in roughly eight to ten hours, versus a week or more by hand.
• As reported by the GitHub Blog: during a roughly four-hour journey, steering the agent from a phone produced a working Maven plugin, a CI pipeline and performance tests.
• A reported Windows-specific Enter-key bug was reproduced through Copilot-driven UI tests and fixed upstream.

As reported by the source (GitHub Blog article); AgentGid did not measure these figures.

The agents used here

GC

GitHub CopilotGitHub (Microsoft) · AI IDEs and editor agents

AI coding assistant from GitHub offering completions, chat and agent mode in IDEs, a terminal CLI, a desktop app and a cloud agent that works on assi…

Price

Free + $10/mo

Gid Score

70 #2 in IDEs

What it does, pricing, alternatives →

Context7Upstash · Agent tooling for cost, context and memory

Gives coding agents up-to-date, version-specific documentation and code examples for libraries, through an MCP server or API, instead of relying on w…

Price

Free + $10/mo

Gid Score

45 #21 in Agent tooling

What it does, pricing, alternatives →

Similar use cases

ShowcaseEmil Stenström

JustHTML: a Python HTML5 parser built with coding agents that passes html5lib tests

A developer spent his off-hours using Copilot agent mode with several models to build a dependency-free HTML5 parser, and wrote up every stage, including a full restart.

JustHTML is about 3,000 lines of Python with 8,500+ tests passing.

GCGitHub CopilotBuilding apps · Testing

Recipe

Bootstrap or upgrade a project with Claude Code using the Vibe Coding Toolkit prompts

A GitHub repository of prompts, templates and docs that lets a terminal-capable coding agent prepare a machine, start a new Next.js project or update an existing one. The repo's a…

A new project ends with a configured foundation, documentation files and the next MVP task identified.

Claude CodeCavemanRTKCodexSuperpowersBuilding apps · Refactoring

Recipe

Generate unit and integration tests with GitHub Copilot

GitHub's tutorial uses Copilot Chat to write a unit test suite for a class, then integration tests that mock an external notification service, and then asks what coverage is still…

A unit test suite that covers edge cases, exceptions and data validation.

GCGitHub CopilotTesting