What it should do, not what it does
A test that records split_bill(1, 2) returning [0, 0] would pass forever. A Breakspec rule says the shares add up to the bill, so it fails.
Compare · Checked 12 October 2026
Breakspec vs Diffblue Cover
Diffblue Cover writes unit tests for Java and Kotlin automatically. The tests record what your code does today, so you find out if that changes later. If your code is already wrong, the tests record the wrong answer as the right one.
What Diffblue Cover does
- Works with Java 8, 11, 17 and 21, and Kotlin, using JUnit or TestNG.
- Diffblue says its tests “capture the current behavior of the code”.
How Breakspec is different
14 languages
Breakspec checks Python, TypeScript, JavaScript, Go, Rust, Java, Kotlin, C, C++, C#, Ruby, PHP, Swift and Elixir.
Made for code from AI agents
When something breaks, the details go back to your agent as a fix request, and Breakspec checks the fix.
| Diffblue Cover | Breakspec | |
|---|---|---|
| What the tests check | What your code does today | What you said it should do |
| If your code already has a bug | The bug becomes the expected answer | A rule fails and shows you an example |
| Languages | Java and Kotlin | 14 |
What Diffblue Cover does better
- It adds a lot of tests to a big Java codebase quickly, with no rules to write.
- Recording what your code does today is exactly what you want before a big refactor.
Can I use both?
Yes. Use Diffblue to lock in behaviour before a refactor, and Breakspec to check that the behaviour is right.
Sources
Checked on 12 October 2026, from Diffblue Cover’s own docs and pricing pages. Prices and features change; if something here is out of date, tell us at sales@breakspec.com and we’ll fix it.
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