Agent Series (21): Harness Testing — 45 Tests, How They're Designed, and What Bugs They Found

Short summary

Deep technical guide to testing agent harness systems with 45 tests across three categories: 19 functional tests verify core behavior and layer ordering, 17 adversarial tests specifically cover injection attacks and privilege escalation vulnerabilities, and 9 chaos tests handle edge cases and budget exhaustion scenarios. Demonstrates test isolation patterns, shared mock state management, and audit logging implementations for reliable agent execution.

• •45 tests organized as 19 functional, 17 adversarial, 9 chaos covering harness security and reliability
• •Teaches test isolation via pytest autouse fixtures and shared mock state management
• •Includes concrete injection payloads and adversarial patterns for agent safety validation

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