Diffblue Cover - AI Agent for Java unit test generation and management - Diffblue

Hype Cycle for AI in Software Engineering, 2025

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The hard truths about generating Java unit test coverage for application modernization

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Modernization depends on coverage

Thorough unit test coverage is the foundation of safe refactoring and application modernization, yet many large Java codebases lack sufficient coverage to move quickly and confidently.

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Automation must scale, not assist

Generating thousands of unit tests fast enough requires automation, but generic LLM coding assistants rely on continuous prompting and manual review, which makes them hard to scale across evolving systems.

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Built for autonomous Java unit testing

Diffblue’s unit test generation agent is designed specifically for this challenge, autonomously producing high-quality Java unit tests that deliver meaningful coverage with minimal ongoing developer effort.

LLM-based coding assistants can do impressive things, but they’re not built to deliver comprehensive unit testing coverage. They don’t reason about full applications, struggle with consistency, and can’t guarantee regression safety across a changing codebase.

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Why generic LLM coding assistants aren’t enough

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AI Coding Assistants

Scope of code understanding

Application-level context and dependencies

Understands full application behavior and cross-class dependencies

Operate primarily at the file or local context level

Approach to test coverage

How coverage is generated and scaled

Automates systematic unit test coverage across the codebase

Generate individual test suggestions without a coverage strategy

Test maintenance over time

How tests evolve as the code changes

Automatically updates or removes tests as application logic changes

Require manual intervention to keep tests aligned with code changes

Execution environment

Where code execution and analysis take place

Runs inside your environment with no source code leaving your systems

Typically rely on external, cloud-hosted LLM services

How Diffblue Cover automates Java unit test coverage end-to-end

Analyze your code, generate meaningful JUnit tests, keep them in sync as the code changes, and track coverage and risk in Cover Reports.

Analyze: Understand your Java application

Cover models classes, methods, and behavior across your codebase to target meaningful test generation.

Generate: Generate meaningful tests

Produces human-readable JUnit tests using program analysis, generated in the IDE, via CLI, or automatically in CI.

Maintain: Keep tests in sync

Updates, adds, or removes tests as behavior changes, keeping regression coverage stable as the code evolves.

Assess: Monitor coverage, risk, and testability

Visualize coverage, coverage risk, and testability in Cover Reports, so teams can prioritize improvements and track progress.

Driving big results for enterprise organizations worldwide

59M +

lines of Java tested

1,000 years

of developer time saved

Up to 250x

faster test creation vs humans

Goldman Sachs complete a year's worth of Java unit test writing overnight with Diffblue Cover

US Aerospace and Defense company accelerates application modernization by using Diffblue Cover

Global Technology Manufacturer reduces failures with Diffblue Cover

US Pension & Retirement System soars to 70% Java unit test coverage using Diffblue Cover

Built for the way Java teams work

Run automated Java unit testing in the IDE for fast iteration, via CLI for scale, and in CI/CD to keep tests current on every merge.

IntelliJ Plugin

Generate Java unit tests interactively in IntelliJ for quick feedback during development.

CLI

Generate and maintain unit tests across large Java projects. Ideal for legacy estates and modernization work.

CI/CD Pipeline Integration

Automatically generate and update unit tests on pull requests/merges to keep regression coverage stable.

Integrates with your Java toolchain

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Who Diffblue Cover is for

Engineering Leaders

Raise and sustain Java unit test coverage while de-risking refactors and modernisation efforts. Improve CI/CD stability by reducing fragile tests and increasing confidence in code changes.

Developers & Test Engineers

Offload repetitive test creation so you can focus on feature development and design work. Use directly in IntelliJ and CI/CD workflows to accelerate delivery without disrupting existing processes.

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Explore our product

Learn more about Cover: the leading AI for Code platform.

Deep-dive resources on Java unit testing

New Benchmark Report: Diffblue Cover vs. Leading AI Coding Assistants

Our 2025 benchmark report reveals critical performance gaps between Diffblue Cover and AI coding assistants. 18 pages of data-driven insights.

Uplifting Test Coverage Out of the Box with Diffblue Cover

For Java teams struggling with coverage gaps, velocity constraints, or legacy code challenges, Diffblue Cover offers a path forward.

The Next Generation of Our Best-In-Class Unit Test Generation Platform

Our next generation of Diffblue Cover represents a fundamental shift in how enterprises address under-tested applications.

Taming Legacy Java: How Agentic AI Transforms Unmaintainable Codebases

Understand the challenges and solutions that will help you confidently test and modernize your legacy Java codebases.

Measuring Success in Java Modernization: Testing, Coverage, and Quality

Gain clarity on why coverage matters, how mutation testing sharpens insight, and how to keep refactored code maintainable.

Gartner® Hype Cycle™ for AI in Software Engineering, 2025

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