Create Skill Test

Scaffold an evaluation spec (eval.yaml) for a skill or agent so it conforms to the Vally schema, passes skill-validator check and check_eval_quality.py, is powerful enough to return a verdict, and does not overfit to the skill's own wording.

When to Use

• Creating a new eval.yaml for a skill or agent
• Adding stimuli to an existing eval
• Sizing an eval so the pass gate can actually be reached
• Setting up or repairing fixture files alongside an eval
• Reviewing whether rubric items and graders risk overfitting

When Not to Use

• Diagnosing a failing or regressed eval — use improve-skill-quality
• Modifying the skill-validator or the evaluation workflows
• Creating or editing SKILL.md files — use create-skill

Inputs

Workflow

Step 1: Locate the target and the test directory

tests/<plugin>/<skill-name>/eval.yaml          # skills
tests/<plugin>/agent.<agent-name>/eval.yaml    # agents (the agent. prefix disambiguates)

Verify the target exists at plugins/<plugin>/skills/<skill-name>/SKILL.md or plugins/<plugin>/agents/<agent-name>.agent.md, and read it.

Agent evals sit outside the verdict flow. The canonical experiment declares evals: tests/*/!(agent.*)/eval.yaml, so agent.* specs are excluded: no verdict is ever computed for them, the stimulus floor does not apply, and ./eng/run-skill-evals.sh drops them even when you name one explicitly (its --eval-filter is intersected with that glob). The distinct-stimulus floor therefore applies to skill evals only. Author agent evals for the scenario coverage and the deterministic graders, and run them as described in Step 10.

Be careful with a skill that sets disable-model-invocation: true. The model cannot invoke it, so the skill is absent from the model-facing skilled arm and any direct eval compares two identical arms. Answer-content graders do not create a difference between those arms. The honest coverage for such skills is dependency-level — through the outcome evals of the skills that load them, and through the plugin arm. For example, filter-syntax is covered by the filtered-command scenarios in tests/dotnet-test/run-tests/eval.yaml.

Step 2: Write the spec skeleton

The spec is Vally format. Every eval in this repo uses stimuli: and graders:; scenarios: and assertions: are a pre-Vally format that no longer loads.

name: <skill-name>
description: Evaluates the <plugin>/<skill-name> skill
type: capability
defaults:
  timeout: 5m
  runs: 1
stimuli:
  - name: <what the agent must accomplish>
    prompt: <natural developer request>
    environment:
      files:
        - src: fixtures/<case>/Project.csproj
          dest: Project.csproj
    graders:
      - type: output-matches
        config:
          pattern: (root cause|underlying issue)
      - type: exit-success
      - type: prompt
    rubric:
      - <outcome the agent should have reached>

defaults: replaces config: — it does not join it. config is a deprecated alias for the same block and vally throws on a spec declaring both. Some existing evals still open with config:; when you change settings, replace it with one defaults: block. The failure is invisible otherwise: the job exits 0 with no verdicts and the PR comment blames "transient infrastructure".

Step 3: Size the eval for power before writing content

The gate gives each distinct stimulus one vote. Repeated runs for one stimulus collapse to one majority-direction vote and remain available as reliability evidence.

1. Distinct stimuli ≥ 5, else the verdict is underpowered — never a pass, never a regression.
2. p ≤ 0.05 on an exact one-sided sign test over discordant (non-tie) stimulus votes. Ties are not discarded; they hold the discordant count down.

At exactly 5 stimuli, one tie is fatal because it leaves 4 discordant votes. At 6 stimuli one tie is survivable; at 7, up to two are. A loss is not. Five is an eligibility floor, not adequate power. For example, 80% power needs 8 discordant votes only for a true 90% conditional win rate; it needs 18 at 80%, 37 at 70%, and 158 at 60%. Size for the effect and tie rate you need to detect.

Use runs for reliability, not task breadth. Vally recommends 3 runs in CI and 5–10 nightly for pass rate, pass@k, pass^k, and flakiness. Extra runs never clear the five-stimulus floor.

Do not set runs in dotnet-skills.experiment.yaml; experiment overrides overwrite every eval's own value rather than defaulting it.

Step 4: Write stimuli

• Name describes what is tested, not how.
• Prompt is a natural developer request. Never mention the skill, the agent, or its vocabulary — cued prompts inflate the overfit score and bias the baseline.
• Each stimulus should discriminate a different property of the skill. Five stimuli covering one property give arithmetic, not evidence.
• Give every stimulus a stable, unique name. Vally pairs comparison trajectories by (stimulus name, trial index); duplicate names make slot identity ambiguous.
• Include a boundary / no-op stimulus for any skill that migrates or rewrites code, proving it leaves already-correct input alone.

Step 5: Configure the environment

environment:
  files:
    - src: fixtures/broken-build/App.csproj      # path relative to eval.yaml
      dest: App.csproj                           # path in the agent's working directory
    - src: fixtures/broken-build                 # a directory
      dest: .
  commands:
    - dotnet build -bl || exit 0                 # guard intentional failures

Do not set environment.skills in a skill eval. The experiment declares vary: /environment/skills and supplies the value itself — [] for the baseline arm and plugins/<plugin>/skills/<skill> for the skilled arm — so anything the eval declares is replaced, in every arm. It cannot add a skill to one arm only. environment.skills is meaningful only in an agent.* eval, which the experiment does not vary; there it is the set of skills the agent may invoke. Copy the shape from an existing agent eval such as tests/dotnet-test/agent.test-quality-auditor/eval.yaml rather than reproducing a remembered form — the specs in this repo are not consistent about how they spell those entries.

Fixture rules — each one has already cost a real result:

• Every referenced fixture must be tracked by git. .gitignore (e.g. coverage*.xml) has silently swallowed a committed fixture: the eval passed locally and failed at setup in CI. Verify with git ls-files, not by looking at the working tree.
• Every fixture must behave as its stimulus assumes. A fixture meant to be healthy must build; a fixture meant to be broken must fail for the exact reason the stimulus is about, and no other. Judges penalize agents for unrelated "pre-existing build issues" that the fixture author introduced.
• Every fixture must reproduce the bug its stimulus is named for. If it does not, the baseline scores well and the skill has nothing to add.
• Coverage fixtures must be internally consistent. A Cobertura report whose declared line-rate, summary totals (lines-covered/lines-valid), and <line> elements disagree lets the two arms read different truths, and the loss is the fixture's fault. Update any rubric item or prompt that quotes a figure in the same change.
• Do not wire duplicate fixtures to raise n; rename leftovers add trials without evidence.
• A setup command that is expected to fail while still producing its artifact must be guarded (|| exit 0), or vally drops the trial.
• A cleanup command that strips sources must skip directories containing SKILL.md — the staged skill lives there, and deleting it aborts only the skilled arm.

Step 6: Write graders

Graders are hard pass/fail checks evaluated on every arm.

Rules:

• A grader whose config is absent or missing its required key parses fine and enforces nothing. The usual cause is an indentation slip during an edit; check_eval_quality.py blocks it.
• Prefer broad patterns that several valid approaches satisfy: (root cause|primary error|underlying issue).
• If the skill mandates an output shape, assert on it. A skill required to emit a decisive Recommendation: line can silently stop doing so while the eval still passes.
• Use file-not-contains / file-not-exists to prove the agent avoided an incorrect action.

Step 7: Write rubric items

Rubric items are judged pairwise (baseline vs. skilled). The overfitting judge classifies each item:

1. Test outcomes, not methods: "Identified the root cause of the build failure", not "Replayed the binlog using dotnet build /flp".
2. Accept any valid approach.
3. Never reference the skill by name, and never reuse SKILL.md phrasing.
4. Never reward using the skill — the harness reports activation separately, so a rubric item that does this measures nothing and inflates the overfit score.
5. Do not test knowledge the model already has; it adds no delta.
6. Keep each item independently evaluable.
7. Do not reward raw volume (test count, report length); judges will compare it when both arms act.

Good:

rubric:
  - Correctly identified the missing NuGet package as the root cause of the build failure
  - Recognized that downstream failures cascaded from that root cause
  - Suggested a concrete fix that resolves it

Overfitted:

rubric:
  - Replayed the binary log using 'dotnet build /flp:v=diag'   # technique
  - Measured cold, warm, and no-op build scenarios             # vocabulary
  - Used the template-comparison skill                         # rewards activation

Step 8: Add constraints sparingly

constraints:
  expect_tools: [bash]
  reject_tools: [edit, create]
  reject_skills: [some-skill]

• expect_tools: [bash] on an advisory question forces a restore or build and converts an answer into a timeout with no quality benefit. Only require tools when the task genuinely needs them.
• reject_tools is the right way to keep a read-only stimulus read-only.

Step 9: Add dormancy guards

A dormancy guard proves the skill stays dormant on an off-target request that superficially matches it. Add one per real "when not to use" boundary: wrong input format, out-of-scope request, incompatible project type, wrong framework version, prerequisite absent.

  - name: Decline dump analysis request
    prompt: |
      I already have a .dmp crash dump from my .NET app. Can you help me
      analyze it to find the root cause of the crash?
    expect_activation: false
    graders:
      - type: output-matches
        config:
          pattern: (out of scope|not cover|does not|cannot|only.*collect)
      - type: prompt
    rubric:
      - Stated that dump analysis is out of scope
      - Did not open or analyze the dump file
      - Did not install analysis tools such as dotnet-dump analyze, lldb, or windbg
      - Suggested the correct alternative

Never combine expect_activation: false with constraints.reject_skills. That forces the skilled arm to run skill-free, making it identical to the baseline; the score is then pure judge noise. Across four evals the same guard scored −0.4, +0.4, +0.4 and 0, and twice cost a skill its pass. expect_activation: false alone is the repo convention.

Guard rubrics verify three things: recognition (why it does not apply), restraint (no workflow, no file changes, no installs), redirection (the correct next step).

Step 10: Validate

dotnet run --project eng/skill-validator/src/SkillValidator.csproj -- check --plugin ./plugins/<plugin>
python eng/eval-quality/check_eval_quality.py
./eng/run-skill-evals.sh <plugin> <skill-name>

For an agent eval, the third command is a no-op: agent.* is outside the experiment's evals: glob. Exercise one by pointing the runner at an experiment file whose glob includes it:

# copy dotnet-skills.experiment.yaml, widen its evals: glob to tests/*/agent.*/eval.yaml
EXPERIMENT_FILE=my-agent.experiment.yaml ./eng/run-skill-evals.sh <plugin>

Read the trajectories rather than the verdict — there is no sign-test result for an agent eval.

check_eval_quality.py blocks eleven structural defect classes that can corrupt a result: missing or untracked fixtures, self-contradicting coverage fixtures, empty grader configs, dormancy guards with reject_skills, sub-floor stimulus counts, duplicate YAML keys or stimulus names, and config:/defaults: collisions. Do not add a new eval to eng/eval-quality/underpowered-allowlist.txt — the gate rejects allowlist entries that are new relative to the base branch.

For the official run, submit a PR review containing /evaluate so it binds to the reviewed commit.

Validation Checklist

• Directory is tests/<plugin>/<skill-name>/ or tests/<plugin>/agent.<agent-name>/
• Spec uses stimuli: / graders:, and exactly one of defaults: or config:
• For a skill eval, at least 5 distinct stimuli exist, with more for the effect and tie rate that must be detected (agent evals are exempt)
• Each stimulus discriminates a different property and has a stable, unique name
• Prompts never name the skill, the agent, or its vocabulary
• Every referenced fixture exists and is tracked by git ls-files
• Every fixture behaves as its stimulus assumes — healthy ones build, deliberately broken ones fail only for the stated reason
• Every grader has its required config key
• Any output shape the skill mandates has a grader
• Rubric items are outcome-shaped and never reward using the skill
• Dormancy guards use expect_activation: false alone
• skill-validator check and check_eval_quality.py pass

Common Pitfalls