Test the Test

Purpose

Use this skill to write, evaluate, and verify tests that prove behavior rather than implementation details.

Core Rule

Tests prove behavior through public seams, not implementation internals.

A test that breaks when you rename an internal variable without changing behavior is testing the wrong thing. A test that passes when the behavior is broken is worse than no test at all.

Vertical Slice Discipline

Write one test. Implement to pass it. Repeat.

For every behavior change with testable logic, write the smallest targeted test and observe it fail for the missing behavior before changing the implementation. Do not write a broad suite for imagined internals before learning from one vertical slice.

WRONG (horizontal):
  RED:   write all tests
  GREEN: write all implementation

RIGHT (vertical):
  RED → GREEN: one test → its implementation → repeat

For a behavior change in existing code:

diagnose → write targeted behavior test → observe RED → implement narrow behavior → observe GREEN

For an extraction or refactor intended to preserve current behavior:

diagnose current behavior → add focused characterization test → observe PASS
→ move logic without changing behavior → observe PASS

A characterization test is not speculative: it pins behavior already present at a durable seam before logic moves. If the slice also changes behavior, characterize the current behavior first, then use a separate observed RED for the behavior change.

Test Quality Checklist

Before accepting a test as complete:

[ ] Test describes behavior, not implementation details
[ ] Test uses a public seam: route, server action, query helper, or pure helper interface
[ ] Test would survive an internal refactor without changing
[ ] Code written is the minimum to pass the current test
[ ] No broad test suite speculates about unverified internal structure
[ ] Test covers at least one failure/rejection case, not just the happy path
[ ] For high-risk seams: failure path, wrong input, unauthorized access are covered

Seam-Specific Test Expectations

The natural-language matcher or routing seam row is load-bearing: test the direction class, not only the first known phrase. Include adversarial object-position vocabulary so a veto or guard does not accidentally reject the operator's intended noun phrase.

Fixture-vs-Deployed Divergence

If correctness depends on fields or environment values supplied by the actual caller, fixture-only proof is not enough.

Examples:

• a shell caller passes readiness fields into a rendered answer builder
• a server action reads runtime configuration from process.env
• a routing seam receives mode/project/thread context from the live send path
• a grounded packet uses rows read by the live assembler

When the live caller matters, the test or captured evidence must exercise the real call path. Hand-shaped fixtures may supplement that proof, but they do not replace it.

Exactly-Once and Concurrency Expectations

For state-changing record-family seams, include tests for:

• replay of the same request
• double-submit from the same UI path
• concurrent attempts where only one winner is allowed
• zero partial records after a losing or failed attempt

If the repository claims exactly-once behavior through a DB transaction or unique constraint, tests must prove that property at the durable record seam, not just through an in-memory guard.

Sad-Path Acceptance Gate (governed crossings)

Every new or changed governed crossing — a server action or route that records a decision, transitions a status, consumes a grant, or creates lineage — requires an explicit sad-path matrix in the builder return. A crossing whose changed behavior has only happy-path tests is an incomplete return, not a reviewable one.

The matrix has one row per failure condition, with these columns:

The mutation-boundary column states, per row, which effects were prevented: no execution, no application, no repo change, no canonical-truth change, no duplicate transition — as applicable to the crossing.

Baseline row set (the starting matrix for any governed crossing):

• malformed input
• unauthorized actor
• missing target record
• stale / already-decided / duplicate action
• partial persistence failure
• external service failure
• secret-bearing error (redacted before it reaches UI, log, or readback)
• conflicting sibling / state
• happy-path regression after hardening

A row may be marked not-applicable with one line of reasoning (e.g. "no external service on this crossing"). An unexplained empty row is a gap, not a pass. This gate applies to new and changed crossings from adoption forward; it is not a retroactive audit of existing code.

Classify the matrix in the Builder return:

• COMPLETE — every applicable row has named evidence and every excluded row has a specific not-applicable reason.
• NOT_APPLICABLE — the slice changes no governed crossing, with the crossing boundary named.
• SAD_PATH_PARTIAL — one or more required cases lack evidence or a valid not-applicable reason; name each missing case. Partial is never silently presented as complete.

Source-String Tests — Guardrails Only

Source-string tests check whether a string, import, or pattern appears in source code. They are guardrails, not behavioral proof.

Use source-string tests for:

• proving a forbidden import is absent
• proving a file does not call fetch, insert, or a route directly
• protecting inertness/non-authority boundaries on contract-only seams
• checking that a display-only surface did not gain a forbidden action keyword

Do not use source-string tests alone for:

• command parsing behavior
• dispatch decisions
• validation output
• readback text selection
• server action success/failure paths
• route authorization
• state transition logic

When source-string tests are the only coverage for complex behavior, flag the gap in the builder return and the reviewer should request behavioral tests.

Database Assertions

For persistence seams, asserting durable database state is the correct proof.

Prefer testing through public seams — routes, server actions, query helpers — rather than querying DB internals directly.

When persistence is the behavior being proven, assert the durable record exists with the correct fields through the same query layer the app uses.

Verification rules

• A verdict is VERIFIED, NOT VERIFIED, or INCONCLUSIVE. Inconclusive is not a pass, and a negative is never hidden.
• When something passes too easily, suspect the observation method before the system. A blank screenshot passes a lazy gate.
• Trust artifacts, not self-reports. When verifying delegated work, inspect the diff, the file, and the runtime behavior. Agents report what they intended, not always what happened.
• A generated artifact that was never executed is a draft, not a deliverable.
• Verify what a dry run actually skips by observing it, not by trusting its name. Some dry runs still touch the network.
• Evidence survives every cleanup, checked at its named location rather than assumed.
• Prefer no new test over a bad test. A bad test mostly tests mocks, encodes current implementation details, depends on timing or global state, needs expensive infrastructure for a small fix, or would be deleted right after proving the fix.

What Makes a Bad Test

• Tests a private function or internal helper directly
• Breaks when you rename an internal variable but behavior is unchanged
• Speculates about implementation structure instead of pinning required or already-observed behavior
• Mocks internal collaborators instead of testing through the interface
• Passes when the actual behavior is broken
• Only tests the happy path when the seam has real failure modes
• Source-string assertion for complex behavior treated as full coverage

Evaluator-side change handling

An evaluator-side change alters what declares pass: a test, fixture, threshold, expected value, sample set, judge prompt, validation route, or evidence path. An implementation-side change alters the behavior being measured.

Evaluator-side and implementation-side changes must stay separately inspectable, so review can determine which one produced the green result. This is a separability requirement on the record, not a limit on diff width; scope rules govern how wide a change may be, not whether the two halves can be told apart. Separate commits, separate sections of the return, or an explicit before-and-after statement of the evaluator all satisfy it. A single undifferentiated change that moves both halves at once does not.

Classify every evaluator-side change:

When the evaluator appears wrong: preserve the original failure and the evaluator's identity, cite the objective or invariant it contradicts, classify the change, route a changed success definition through reconvergence, compare old and new evaluator behavior on positive and negative controls, and rerun the original case plus one non-equivalent check. A positive control must still pass and a negative control must still fail under the new evaluator; an evaluator change that silences the negative control is a defect, not a repair.

Non-equivalent discriminating evidence

Where the visible signal is controlled by the same change that is being accepted, at least one check must be non-equivalent to that signal. Re-running a second command over the same manipulated signal is not independent evidence.

Already owned elsewhere and referenced here rather than restated: re-running the original failure, real-caller-path evidence (Fixture-vs-Deployed Divergence above), a clean-baseline rerun, negative and denied-path proof for high-risk seams, independent review, and owner verification on the real surface.

Options for the non-equivalent check:

• held-out inputs the change did not target;
• counterfactual: break the behavior on purpose and confirm the check fails;
• metamorphic: a transformation of the input whose expected effect on the output is known independently of the implementation;
• property-based: an invariant asserted over generated inputs rather than chosen ones; and
• proxy perturbation: perturb or hide the visible proxy and confirm the intended behavior still holds.

Model-graded evaluators. Where an LLM judge or model-scored rubric is load-bearing and the executor can influence its input through text, the rubric must be assembled or sanitized independently of executor-controlled text. Candidate-supplied text must not reach the rubric, the grading instructions, or the judge's notion of success unfiltered.

Objective integrity, Level A

When a test, metric, rubric, benchmark, judge, or other proxy is load-bearing for accepting a change, record three lines in the return before claiming success:

TRUE OBJECTIVE:
STRONGEST APPARENT-SUCCESS SHORTCUT:
DISCRIMINATING CHECK:

Passing a proxy is evidence about the objective, not proof the objective was achieved. Name the strongest route by which the change could pass while leaving the objective unmet, and the check that would catch it.

Stop at Level A when the discriminating check is already mandatory, independent of this change, and capable of failing the strongest shortcut named above.

Materiality gate. Technical editability alone never escalates routine work. Being able to edit an in-tree test is not by itself a reason to escalate, or every implementation would escalate. Repeated failure or budget pressure raises scrutiny only when paired with a load-bearing evaluator this change can modify. Pressure is a risk signal, never a diagnosis, and never a claim about intent.

Escalate beyond Level A only when the Level A check is inadequate and a material condition holds:

1. acceptance materially relies on an evaluator, environment, or evidence surface this change may modify under current scope;
2. the strongest plausible shortcut is not already defeated by a mandatory independent check;
3. the change touches a load-bearing evaluator, fixture, threshold, expected value, sample set, judge prompt, validation route, or evidence path;
4. the objective and the acceptance conditions appear mutually unsatisfiable;
5. observable evidence suggests evaluator gaming, environment tampering, or evidence shaping; or
6. a reviewer or pressure-tester requests it.

When escalation applies, load reference/objective-integrity.md for the Level B decision model, escalation handling, and non-claim boundary. Do not reconstruct those rules here.

Return Requirement

Include in the unified return block when this skill fires:

Test the Test:
- Seam type tested:
- Behavioral tests added: yes/no / list
- Failure/rejection path covered: yes/no
- Source-string tests used: yes/no — guardrails only / for complex behavior (flag)
- Test gaps remaining:

Performance and resource boundaries

A changed seam also reports its resource behavior, because a passing functional test says nothing about cost:

Performance / resource boundaries:
- N+1 queries or repeated remote calls introduced: Yes / No
- Unbounded list/search/read/loop introduced: Yes / No
- Blocking work added to a latency-sensitive path: Yes / No
- Unbounded client work or repeated rendering introduced: Yes / No
- Evidence: <measurement, named test/inspection, or specific not-applicable basis>

Treat a performance concern as blocking only when the change creates a credible correctness, availability, cost, or operator-usability risk. Speculative micro-optimization is not a gate.