Create Skill Test

Create Skill Test

This skill helps you scaffold evaluation tests (eval.yaml) for agent skills, ensuring they conform to the dotnet/skills repository conventions, pass the skill-validator checks, and avoid common overfitting pitfalls.

When to Use

• Creating a new eval.yaml test file for a skill
• Adding scenarios to an existing eval file
• Setting up test fixture files alongside eval definitions
• Reviewing whether rubric items and assertions risk overfitting

When Not to Use

• Running or debugging existing tests (use the skill-validator directly)
• Modifying the skill-validator tool itself
• Creating or editing SKILL.md files (use the create-skill skill)

Inputs

Workflow

Step 1: Locate the skill and determine the test directory

Tests live at:

tests/<plugin>/<skill-name>/eval.yaml

Verify the skill exists at plugins/<plugin>/skills/<skill-name>/SKILL.md. Read the skill content to understand what it teaches — this is critical for writing non-overfitted rubric items.

Step 2: Create the test directory and eval.yaml

Create the directory and file:

tests/<plugin>/<skill-name>/
└── eval.yaml

Step 3: Write scenarios

Each scenario needs a name, prompt, at least one assertion, and a rubric. Use this structure:

scenarios:
  - name: "Descriptive scenario name"
    prompt: "Natural language task description as a developer would phrase it"
    setup:
      copy_test_files: true          # OR use inline files
    assertions:
      - type: "output_contains"
        value: "expected text"
    rubric:
      - "The agent correctly identified the root cause"
      - "The agent suggested a concrete, actionable fix"
    timeout: 120

Scenario guidelines

• Name: Describe what is being tested, not how (e.g., "Diagnose missing package reference" not "Test binlog replay and error extraction").
• Prompt: Write as a natural developer request. Never mention the skill name or instruct the agent to "use a skill." Neutral prompts prevent prompt overfitting.
• Timeout: Default is 120 seconds. Use 300-600 for scenarios requiring builds, benchmarks, or multi-step operations.

Step 4: Configure setup

Choose one of three setup strategies:

Option A: Copy test files (recommended for complex fixtures)

Place fixture files alongside eval.yaml and enable auto-copy:

setup:
  copy_test_files: true

All files in the directory (except eval.yaml) are copied into the agent's working directory.

Option B: Inline files (good for small, self-contained scenarios)

setup:
  files:
    - path: "MyProject/MyProject.csproj"
      content: |
        <Project Sdk="Microsoft.NET.Sdk">
          <PropertyGroup>
            <TargetFramework>net10.0</TargetFramework>
          </PropertyGroup>
        </Project>
    - path: "MyProject/Program.cs"
      content: |
        Console.WriteLine("Hello");

Option C: Reference fixture files from a subdirectory

setup:
  files:
    - path: "TestProject.csproj"
      source: "fixtures/scenario-a/TestProject.csproj"

Use this when multiple scenarios share a fixtures/ directory with separate subdirectories.

Setup commands (optional)

Run shell commands before the agent starts (e.g., to build a project and generate artifacts):

setup:
  copy_test_files: true
  commands:
    - "dotnet build -bl:build.binlog"

Step 5: Write assertions

Assertions are hard pass/fail checks. Use them for objective, binary-verifiable criteria.

Assertion guidelines

• Prefer broad assertions that multiple valid approaches would satisfy.
• Avoid narrow assertions that gate on a specific syntax or flag the LLM already knows.
• Use output_matches with regex alternation for flexible matching: "(root cause|primary error|underlying issue)".
• Use file_contains / file_not_contains to verify the agent modified files correctly.
• Use output_not_contains and file_not_exists to verify the agent avoided incorrect actions.

Step 6: Write rubric items

Rubric items are evaluated by an LLM judge using pairwise comparison (baseline vs. skill-enhanced). Quality metrics (rubric-based at 40% weight plus overall judgment at 30%) together dominate the composite improvement score.

The three rubric classifications (and how to stay in "outcome")

The overfitting judge classifies each rubric item:

Rubric writing rules

1. Test outcomes, not methods. Write "Identified the root cause of the build failure" — not "Replayed the binlog using dotnet build /flp."
2. Allow alternative approaches. If multiple valid solutions exist, the rubric item should accept any of them.
3. Never reference the skill by name or use phrasing copied directly from the SKILL.md.
4. Don't test pre-existing LLM knowledge. If the LLM already knows something (common APIs, standard syntax, basic escaping), testing for it adds no signal.
5. Test findings, not diagnostic steps. Write "Correctly determined that the root cause is a missing PackageReference" — not "Used dotnet restore to check package resolution."
6. Each item should be independently evaluable. Avoid compound items that test multiple things.

Examples

Well-designed (outcome-focused):

rubric:
  - "Correctly identified the missing NuGet package as the root cause of the build failure"
  - "Recognized that downstream project failures were cascading from the root cause, not independent errors"
  - "Suggested a concrete fix that would resolve the root cause"

Overfitted (vocabulary/technique):

rubric:
  - "Replayed the binary log using 'dotnet build /flp:v=diag'"      # technique: gates on specific command
  - "Measured cold, warm, and no-op build scenarios"                  # vocabulary: uses skill's labels
  - "Used the --clreventlevel flag with dotnet trace collect"         # vocabulary: gates on specific flag

Step 7: Add optional constraints

expect_tools: ["bash"]           # Agent must use these tools
reject_tools: ["create_file"]    # Agent must NOT use these tools
max_turns: 10                    # Maximum agent iterations
max_tokens: 5000                 # Maximum token budget

Use constraints sparingly — only when the scenario specifically requires or forbids certain agent behaviors.

Step 8: Add non-activation scenarios with expect_activation: false

Many skills have clear boundaries — situations where the skill should recognize it does not apply and decline gracefully. Test these boundaries using expect_activation: false.

How expect_activation: false works

When a scenario has expect_activation: false:

1. All three runs still execute (baseline, skilled-isolated, skilled-plugin) and assertions are evaluated on each. The flag does not change which runs are performed.
2. Activation verdict is inverted — if the skill is not activated for this prompt, the evaluator reports it as ℹ️ not activated (expected) instead of treating it as a failure.
3. The scenario is excluded from the noise test — the multi-skill activation test only runs positive (expect_activation: true) scenarios.

When to use non-activation scenarios

Add expect_activation: false scenarios when the skill has explicit "When Not to Use" boundaries. Common patterns:

Example: Wrong input format

- name: "Reject iOS crash log as wrong format"
  prompt: "I have a crash log file at crashlog_ios.txt from a crashed app. Please symbolicate the .NET runtime frames."
  expect_activation: false
  setup:
    copy_test_files: true
  assertions:
    - type: "output_matches"
      pattern: "(iOS|Apple|not.*(Android|tombstone)|wrong.*(format|type))"
  rubric:
    - "Recognized that this is an iOS crash log, not an Android tombstone"
    - "Did NOT attempt to apply the Android tombstone symbolication workflow"
    - "Explained that iOS crash logs require a different symbolication process"

Example: Out-of-scope request

- name: "Decline dump analysis request"
  prompt: |
    I already have a .dmp crash dump file from my .NET app. Can you help
    me analyze it to find the root cause of the crash?
  expect_activation: false
  assertions:
    - type: "output_matches"
      pattern: "(out of scope|not cover|does not|cannot|only.*collect)"
  rubric:
    - "Clearly states that dump analysis is out of scope for this skill"
    - "Does not attempt to open or analyze the dump file"
    - "Does not install analysis tools like dotnet-dump analyze, lldb, or windbg"
  timeout: 30

Example: Incompatible project type

- name: "Decline CPM conversion for packages.config project"
  prompt: "Convert my simple-packages-config/LegacyApp project to Central Package Management."
  expect_activation: false
  setup:
    copy_test_files: true
  assertions:
    - type: "output_contains"
      value: "packages.config"
    - type: "file_not_exists"
      path: "simple-packages-config/Directory.Packages.props"
  rubric:
    - "Detected the project uses packages.config instead of PackageReference format"
    - "Informed the user that CPM requires PackageReference and cannot be applied to packages.config projects"
    - "Suggested migrating from packages.config to PackageReference first"
    - "Did not attempt to create Directory.Packages.props or modify any project files"

Rubric guidelines for non-activation scenarios

Non-activation rubric items typically verify three things:

1. Recognition — The agent identified why the skill doesn't apply.
2. Restraint — The agent did NOT attempt the skill's workflow (no file modifications, no tool installs).
3. Redirection — The agent suggested the correct alternative approach or next step.

Step 9: Validate the eval.yaml

Run the static validator:

dotnet run --project eng/skill-validator/src/SkillValidator.csproj -- check --plugin ./plugins/<plugin>

Then run evaluation (at least 3 runs for reliable results):

dotnet run --project eng/skill-validator/src/SkillValidator.csproj -- evaluate \
  --runs 3 \
  --tests-dir tests/<plugin> \
  plugins/<plugin>/skills/<skill-name>

eval.yaml Template

scenarios:
  - name: "<Describe what the agent should accomplish>"
    prompt: "<Natural developer request — do not mention the skill>"
    setup:
      copy_test_files: true
    assertions:
      - type: "output_contains"
        value: "<key term that a correct response must include>"
      - type: "exit_success"
    rubric:
      - "<Outcome: what the agent should have identified or produced>"
      - "<Outcome: what fix or recommendation the agent should have given>"
      - "<Outcome: what incorrect approach the agent should have avoided>"
    timeout: 120

  - name: "<Describe situation where the skill should NOT apply>"
    prompt: "<Request that superficially matches the skill but falls outside its scope>"
    expect_activation: false
    setup:
      copy_test_files: true
    assertions:
      - type: "output_matches"
        pattern: "<pattern matching the agent's explanation of why it cannot help>"
      - type: "file_not_exists"
        path: "<file the skill would create if it incorrectly activated>"
    rubric:
      - "<Recognition: agent identified why the skill does not apply>"
      - "<Restraint: agent did not attempt the skill's workflow>"
      - "<Redirection: agent suggested the correct alternative>"
    timeout: 120

Validation Checklist

After creating a test, verify:

• Test directory matches tests/<plugin>/<skill-name>/
• Skill exists at plugins/<plugin>/skills/<skill-name>/SKILL.md
• Every scenario has name, prompt, at least one assertion, and rubric items
• Prompts are written as natural developer requests (no skill references)
• Assertions are broad enough that multiple valid approaches pass
• Rubric items test outcomes, not specific techniques or vocabulary
• Fixture files are present when copy_test_files: true is used
• source paths in setup files point to existing fixture files
• Timeouts are reasonable for the scenario complexity
• Non-activation scenarios use expect_activation: false and verify recognition, restraint, and redirection
• dotnet run --project eng/skill-validator/src/SkillValidator.csproj -- check passes

Common Pitfalls