Diffblue

Diffblue is a UK-based AI startup that offers tools to write code for software development. Spun out from the Oxford University AI research group in 2016, Diffblue is automating coding tasks like unit testing, allowing developers to focus on creativity and software functionality.

The firm’s flagship product, Diffblue Cover, uses proprietary AI software and accelerates software delivery by writing Java unit tests (tests for individual software components) in a fraction of the time required by a human developer, as claimed by the company. Unit tests are used to validate application behavior, such as when reviewing code changes, enabling developers to identify bugs or regressions when an unexpected change in application behavior is encountered. Cover automatically maintains its test coverage as code is updated, supporting continuous integration (CI) and DevOps.

Cover is available as a standalone command line interface (CLI) tool or a plug-in for the Java IntelliJ IDE and offers the following features:

1) Cover Core: Autonomously compiles and runs unit tests to validate Java application behavior

2) Cover Report: Generates actionable insights on codebases, including unit test coverage reports and information on code quality, testability, and complexity

3) Cover Optimize: Minimizes the time required to test changes by running only unit tests required to validate the code change

4) Cover Refactor: Rewrites code to optimize observability and testability, expands coverage by writing tests for newly testable code

Compared to other AI-powered coding tools, which generally offer code suggestions or auto-complete functionality and require human input to write finished code, Diffblue’s solution writes new test code autonomously, leveraging unsupervised reinforcement learning instead of pre-trained transformers. Cover runs entirely within an organization’s local environment and does not pull code from external repositories, utilizing only the codebase of the applications within its coverage.

In September 2020, Diffblue launched a free community version of its Cover product, offering limited access to its IntellJ plug-in. In 2024, it was made available on GitHub and GitLab platforms.

Key customers and partnerships

As of May 2024, Diffblue’s customers included Goldman Sachs, Citi, JP Morgan, S&P Global, OPERS, Raytheon, and Cisco.