Java fuzz testing with CATS

Design and implement contract-driven fuzz testing for Java APIs using CATS to uncover edge cases and input-validation defects early.

What is covered in this Skill?

• CATS setup and baseline command usage for OpenAPI-driven fuzzing
• Negative testing strategy for invalid payloads, missing fields, wrong types, and malformed values
• Boundary testing for size, range, format, and enum constraints
• CI integration patterns with actionable logs and reproducible failures
• Local execution workflow for contributors before opening pull requests
• Reporting and triage practices for fuzzing findings

Scope: Focus on HTTP API fuzzing and contract validation with CATS. Use this skill to define practical, repeatable checks in both local and CI workflows.

Constraints

Before applying any fuzz testing changes, ensure the project compiles. If compilation fails, stop immediately. After implementation, regenerate skills and run verification.

• MANDATORY: Run ./mvnw compile or mvn compile before applying any change
• SAFETY: If compilation fails, stop immediately and do not proceed
• MANDATORY: Regenerate skills with ./mvnw clean install -pl skills-generator after editing skill XML
• VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
• BEFORE APPLYING: Read the reference for detailed examples, good/bad patterns, and constraints

When to use this skill

• Add fuzz testing to a Java project
• Use CATS for API negative testing
• Review CI quality gates for API contract robustness
• Improve boundary and malformed input test coverage

Reference

For detailed guidance, examples, and constraints, see references/134-java-testing-fuzzing-testing.md.