Ask any developer what they dread most about maintaining a large Java codebase, and unit testing will be near the top of the list. Writing unit tests manually is a repetitive and time-consuming task. Yet, you can’t skip it since bugs can easily slip into production if you don’t have good code coverage.
That’s why teams are turning to tools like Diffblue Cover AI test generation to handle the dull parts and keep coverage high. It takes care of the burden of writing tests off the developer’s plate, allowing them to focus on solving real problems.
What is Diffblue Cover?
Diffblue Cover is an AI system for generating Java unit tests. Instead of relying on large language models that “predict” code, Diffblue uses reinforcement learning. In plain terms, that means the tests it writes aren’t just suggestions; they actually compile, run, and validate behavior correctly.
Security-conscious teams will also appreciate that it can run entirely within your environment. No snippets of source code are shipped off for model training.
In practice, you keep coding as usual. Diffblue Cover quietly builds out the safety net, adding tests for methods, classes, and even whole projects, depending on your setup.
Key Features
Works where you do
With Diffblue Cover, AI test generation plugged into IntelliJ, a single click writes a JUnit test in seconds.
CI-ready
Plugins exist for Jenkins, GitHub Actions, GitLab, Azure Pipelines, and AWS CodeBuild. So every commit lands with fresh tests.
Clean output
The tests are standard Java (JUnit 4/5 or TestNG). They read like code you’d write yourself. So tweaking or extending them is easy.
See the gaps
Teams and Enterprise editions add Cover Reports dashboards that track total coverage and highlight holes.
Speed up CI
Enterprise users get Cover Optimize, which skips untouched tests and runs only what matters after each change, reducing build times.
Cover Refactor makes code testable
If legacy code is hard to unit-test, the Refactor module suggests (and can auto-apply) safe, small refactors that open the door to better tests.
New Spring Boot deep support
Recent releases handle XML context configs and @MockBean setups. So, Spring projects come with more comprehensive tests out of the box.
Who is Using Diffblue Cover?
Diffblue isn’t a niche experiment. Major players, including Goldman Sachs, JPMorgan, Citi, Cisco, AstraZeneca, ING, and S&P Global, already use it across their Java systems. These are codebases with millions of lines and decades of history, where manual test writing alone would be impossible to sustain.
Individual developers start with the Community Version, and a small team can use the Developer Plan for daily testing within IntelliJ.
The other common adopters are startups that are modernizing legacy applications or moving to the cloud, as sometimes the first step of breaking up old monoliths is to improve test coverage.
What Makes Diffblue Cover Unique?
There are plenty of AI tools promising to “help with testing,” but Diffblue Cover distinguishes itself in a few key ways.
- The reinforcement learning provides a high level of reliability that language-model-based assistants can’t guarantee. The tests aren’t probabilistic guesses; they’re executable and correct.
- Companies can keep everything on-premises, avoiding the risks of source code leaving the building.
- With over 59 million lines of code already covered and nearly a thousand developer-years of time saved, it has proven that it can handle real-world, complex systems.
Pricing
Diffblue has several ways to get started:
Community Edition (Free)
- IntelliJ plugin only
- Limited to 25 methods under test per month.
Developer Plan ($30/month or $330/year)
- For individual devs & small teams.
- AI test generation for classes & methods
- IntelliJ plugin
- 100 methods under test per month (additional tiers available)
Teams Plan ($30K/year)
- Everything in Developer
- CLI support
- CI pipeline integration
- Analytics dashboards
- Unlimited tests for projects up to 250,000 lines of code.
Enterprise Plan (Custom)
- For very large or regulated organizations.
- Includes everything in Teams
- Cover Optimize
- Enterprise SLAs
- Support for codebases beyond 250,000 lines.
Conclusion
Manual unit test writing has slowed projects for decades. Automating it doesn’t just save time; it raises quality, accelerates delivery, and makes developers’ jobs more enjoyable.
Diffblue Cover automates and makes unit testing dependable, providing maintainable and accurate tests that do not require the manual grind typically needed to create them.
Whether you’re an individual developer tired of boilerplate or an enterprise with millions of lines of code, Diffblue offers a path to stronger software and faster delivery. In a world where shipping speed and code quality often compete, Diffblue Cover shows you can have both.
