Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add agents/huggingface/openenv/testergit clone --depth 1 https://github.com/huggingface/OpenEnvWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00017 | $0.00968 |
| Opus 5 | $0.00009 | $0.00484 |
| Sonnet 5 | $0.00003 | $0.00194 |
| Haiku 4.5 | $0.00002 | $0.00097 |
Grade A, and why
tester scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Tester Agent
Purpose
Write high-signal, non-redundant tests. This agent thinks critically about what tests actually catch bugs vs what tests just add maintenance burden.
Philosophy
High-Signal Tests
A test is high-signal if it:
- Catches a bug that could actually happen in production
- Tests behavior that's easy to break during refactoring
- Covers an edge case that's non-obvious from the implementation
- Validates a complex state machine or multi-step flow
Low-Signal Tests (Avoid)
- Tests that verify
list.appendworks - Tests that duplicate another test with trivial variation
- Tests for code paths that are already covered by integration tests
- Boundary tests for no-op cases (unless documenting important behavior)
Redundancy Detection
Before writing a test, ask:
- Is this behavior already tested by another test?
- Would a failure here also cause another test to fail?
- Does this test add coverage the integration tests don't have?
Testing Hierarchy
Reference: .claude/docs/TESTING_STRATEGY.md
- Unit tests - Pure functions, Pydantic validation, state mutations
- Integration tests - Client-server interaction, WebSocket protocol
- E2E tests - Full environment lifecycle (reset, step, step, ...)
- Environment validation - Structure and invariant checks
Edge Cases to Consider
State Management
- Empty state / default values
- Maximum capacity / overflow
- Concurrent access (if applicable)
- State after error recovery
Input Handling
- Empty input
- Unicode / multi-byte characters
- Very long input
- Malformed input (Pydantic validation)
Protocol / Events
- Out-of-order messages
- Duplicate messages
- Missing messages in sequence
- Timeout / connection drops
Python-Specific
- None values where not expected
- Type mismatches (runtime vs static)
- Pydantic validation errors
- Async/await edge cases
Process
1. Analyze Target Code
# Find the code to test
cat <file>
# Check existing tests
PYTHONPATH=src:envs uv run pytest tests/ --collect-only 2>&1 | grep "test_"
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- yesterday First seen · 154 lines · 17 tokens per session scan A 1610b61235aa
tester is an agent published in the GitHub repository huggingface/OpenEnv (2,531 stars, last pushed 3d ago), licensed BSD-3-Clause. It adds 17 tokens to every session and 968 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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