Diffblue Cover Core

The AI for Code engine at the center of the Diffblue Cover platform

AI for Code: Write Java Unit Tests Automatically

Cover Core uses AI to automatically write human-like JUnit or TestNG tests that are indistinguishable from those written by a developer. Diffblue's AI-written unit tests are ready to use; they compile, run and accurately validate the current behavior of your code.

Cover Core is fully autonomous. It creates an entire unit test suite for your whole application in a single execution - raising coverage levels fast without any developer overhead. Cover Core also maintains this unit test suite as software evolves, even on applications with millions of lines of code. Each test takes just a few seconds to write, compared to tens of minutes for a human developer.

With Diffblue Cover Core you can find bugs sooner, deploy code changes faster, stop worrying about quality gates and coverage levels, and minimize tedious, unproductive developer effort.

Increase unit test coverage

Cover Core automatically writes entire unit test suites to achieve the unit test coverage you need for safe, fast code changes; even in legacy applications.

Minimize maintenance effort

Development teams with good coverage still spend huge amounts of time on unit testing. Cover Core eliminates manual test maintenance so more coverage doesn’t mean more work.

Work 24/7 

Cover Core integrates into your CI pipeline, enabling you to build and deliver software on whatever schedule you need, wherever your teams are located.  

Go beyond the happy path

Cover automatically writes unbiased unit tests that exercise the actual behavior of your code, including obscure corner cases and scenarios developers may not know how to test.

Document your code

The Cover Core unit tests describe every behavior of every method - effectively documenting your code to make future code changes quicker and reduce regressions.

Code stays private

Cover Core’s reinforcement learning AI operates entirely within your network. No data ever leaves your organization.

How It Works

Cover Core uses AI to analyze the bytecode of the methods in your application and automatically write associated unit tests. It determines all the different ways to call each method to cover all of the code, so each unit test fully describes a single behavior of a single method - ready to catch any behavioral change. Every time Cover Core finds a new or different path following a code change it produces a new test, including the method call and all of the necessary assertions.

Diffblue Cover Wrote This Code Automatically

The tests written by Diffblue Cover are complete, human-readable and ready to run. Diffblue Cover Core wrote this unit test, which tests the upload of a file to an AWS S3 bucket, completely automatically in just a few seconds.

It’s not magic, it’s A.I.

Reinforcement learning to be precise.

Index application

Diffblue analyzes the project to determine the structure of your application, builds a map of classes and methods.

Create test candidates

Diffblue creates a test candidate for each unit-testable method in your application.

Evaluate test candidates

Diffblue runs the test candidates to check how good they are.

Determine highest reward

Diffblue predicts which changes to the candidate tests will trigger additional branches to produce higher coverage. Repeat until a suitable test suite has been found.

Our CLI is great for teams working together


What is Diffblue Cover?

Diffblue Cover creates suites of unit tests that run in your continuous integration pipeline between versions and protect against regressions, so you can catch errors faster and earlier in the software development lifecycle. To learn more, see our our product page.

What are the benefits of using Diffblue Cover?

Diffblue Cover helps your team increase automation of your CI pipeline.

For development teams, this:

  • improves velocity and quality of the software you deliver
  • frees up time to focus on creating new features

For DevOps teams, this:

  • helps catch errors and issues earlier (shift left!)
  • improves deployment frequency, lead time, and mean time to repair (MTTR)

Will the tests find regressions in my code?

Yes. Diffblue Cover quickly generates tests that will allow you to adopt CI. The generated tests will help developers quickly identify regressions in subsequent commits before committing new versions.

What are the requirements for running Diffblue Cover?

See the product datasheet for more information.

How can I learn more about customers using Diffblue Cover?

See our case study on how Goldman Sachs has benefited from using Diffblue Cover to increase coverage and create a safety net against regressions.

For example of other ways our customers use Diffblue Cover, click here.

How do we maintain Diffblue unit tests in the future?

Diffblue regression suites are maintained automatically and updated with each new code version to capture the current behavior of the code.

How does Diffblue Cover help me adopt Continuous Integration?

Diffblue Cover AI analyzes your code and writes Java unit tests that run in a CI pipeline after each commit. Cover’s tests:

  • Always compile
  • Run quickly
  • Detect regressions from previous versions
  • Improve coverage
  • Are easy to understand

Should our team stop writing unit tests after adopting Diffblue Cover?

No. Diffblue Cover is meant to complement your own unit tests and help you catch regressions.

How is a unit test different from a Diffblue regression suite?

Developers write individual unit tests to test specific functionality. Diffblue regression suites are generated automatically to help find regressions early in the development cycle. Find out more in our Unit Regression Tests eBook.