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 skills/dr-code/tessera/test-driven-developmentnpx skills add dr-code/tessera --skill test-driven-developmentgit clone --depth 1 https://github.com/dr-code/tesseraWhat 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 | $0.00758 |
| Opus 5 | $0.00009 | $0.00379 |
| Sonnet 5 | $0.00003 | $0.00152 |
| Haiku 4.5 | $0.00002 | $0.00076 |
Grade A, and why
test-driven-development 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 — 110 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development (TDD)
Overview
Write the test first. Watch it fail. Write minimal code to pass.
Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.
Violating the letter of the rules is violating the spirit of the rules.
The Iron Law
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
Write code before the test? Delete it. Start over.
No exceptions:
- Don't keep it as "reference"
- Don't "adapt" it while writing tests
- Delete means delete
Tessera: Discover Existing Test Patterns First
Before writing any test — if tessera MCP is configured in this session:
1. graph_continue (mandatory first call)
2. graph_retrieve with "<feature> test" as query
3. graph_read the nearest existing test file for the module you're testing
This ensures your new test follows the project's established patterns — fixture style, assertion format, naming conventions — instead of inventing something inconsistent.
Also check:
- Are there shared test fixtures in
conftest.pyor similar? - Does the project use real DB instances or mocks for this layer?
- What is the expected assertion style (bare
assert,pytest.raises, custom matchers)?
Red-Green-Refactor
RED — Write Failing Test
Write one minimal test showing what should happen.
Test: exactly one specific behavior
Assert: expected output or state change
Run: verify it FAILS with the right error
If it passes before you write the implementation: the test is wrong. Delete it, re-examine the behavior, rewrite.
If it fails with the wrong error: the test is testing the wrong thing. Fix the test first.
GREEN — Write Minimal Code
Write the minimum code to make the test pass. Nothing more.
"Minimum" means:
- No extra error handling
- No extra features
- No optimizations
- Just enough to pass the test
Run all tests. Verify only the intended tests pass. No regressions.
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 · 110 lines · 17 tokens per session scan A fba9532df8d8
test-driven-development is a skill published in the GitHub repository dr-code/tessera (1 stars, last pushed 21d ago), licensed MIT. It adds 17 tokens to every session and 758 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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