Karat Labs Templates: Bundle Challenges, Tests, and CI in One File

Why a Single File Makes Sense for Coding Challenges

When a hiring team creates a new interview problem, the usual workflow involves several moving parts: a problem statement in a markdown file, a separate JSON or YAML file for test cases, and a reference solution that lives in yet another folder. Each file is a potential source of drift—one file might be updated while another is left stale, leading to confusing feedback for candidates.

Karate Labs’ template format solves this by combining all of those pieces into a single JSON or YAML document. The schema declares the problem title, description, input/output specifications, sample tests, and even an optional reference solution. Because the entire challenge lives in one place, there’s no chance of mis‑alignment between the statement and the tests that the grading system will run.

Declarative Structure: What the Schema Looks Like

The core of a template is a JSON or YAML object with the following top‑level keys:

• title – Human‑readable name of the challenge.
• description – A concise problem statement.
• tests – An array of test objects, each with input and output fields.
• solution (optional) – A string of code in the target language, used for automated grading.
• metadata (optional) – Additional fields such as difficulty or tags.

Below is a minimal example in JSON. The same structure works verbatim in YAML, just change the syntax.

{
  "title": "Sum of Two Numbers",
  "description": "Return the sum of two integers.",
  "tests": [
    {"input": [1, 2], "output": 3}
  ],
  "solution": "def sum(a, b): return a + b"
}

From Authoring to CI: One Command, One Pipeline

Once you have a template file—let’s call it challenge.karat.json—you can validate and execute it locally with the karat CLI:

1. Ensure you have the CLI installed (see Karat Labs documentation for installation).
2. Run karat validate challenge.karat.json to check schema compliance. The command will fail if any required field is missing or if the test objects are malformed.
3. Execute karat test challenge.karat.json to run the embedded tests against the optional reference solution. The output will show pass/fail status for each test case.

Because the template is a single file, you can add it to a Git repository and hook it into a GitHub Actions workflow. A minimal .github/workflows/karat.yml might look like this:

name: Karat CI
on: [push]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '18'
      - name: Install Karat CLI
        run: npm install -g karat
      - name: Validate template
        run: karat validate challenge.karat.json
      - name: Run tests
        run: karat test challenge.karat.json

This workflow automatically validates the schema and runs the tests every time the template file is pushed, ensuring that any new challenge is immediately test‑driven and ready for candidate grading.

Trade‑Offs and Practical Considerations

• Schema Evolution: Karat’s schema is versioned. If you upgrade the CLI, older templates may become invalid. It’s a good practice to run karat migrate (if available) or manually update the schemaVersion field when a new CLI version is released.
• Learning Curve: Authors accustomed to separate markdown and JSON files need to adjust to a single JSON/YAML document. A quick cheat sheet or template skeleton can reduce friction.
• Optional Reference Solution: Including a solution can speed up grading, but it also exposes the answer to candidates if the repository is public. Use private repos or carefully control access.
• CLI Access: Full validation and test execution require the paid Karat CLI. Free tiers may allow only schema validation, so plan accordingly.

How to Verify Your Setup Without Running a Full CI Pipeline

Before committing to a GitHub Actions integration, you can perform a quick sanity check locally:

1. Run karat validate challenge.karat.json and confirm no errors.
2. Run karat test challenge.karat.json and ensure the test passes.
3. Open the file in a JSON/YAML linter to catch formatting mistakes that might not trigger the CLI.

Once these steps succeed, you can push the file to your repo and run the GitHub Action to see the full CI cycle in action.

Actionable Takeaway

Adopting Karat Labs’ template format can reduce authoring friction, eliminate test drift, and integrate seamlessly with GitHub Actions for rapid, automated feedback. Start by migrating one existing challenge into the new schema, run the local validation and test commands, then add a simple GitHub workflow. From there, scale the practice to your entire challenge library and enjoy a single source of truth for every interview problem.