Theodore Calvin's Testing Framework (tc)

"In the AI age, specifications and tests are permanent while implementations are disposable."

What is Differential Testing?

Differential testing compares actual output against expected output. No assertions, no matchers, no framework magic - just a diff.

Philosophy

Tests are nothing more than a script that takes input.json and produces output.json, which is then diffed against expected.json. This simple model:

• •Makes tests language-agnostic - the same test suite validates any implementation
• •Separates what (the spec) from how (the implementation)
• •Treats test suites as specifications, not just validation

Core Concept

input.json → run → output.json ←→ diff ←→ expected.json

1. •Your code reads input.json from stdin
2. •Your code writes JSON to stdout
3. •The framework compares output with expected.json

JSON Comparison Rules

• •Objects are order-invariant - {"a":1,"b":2} equals {"b":2,"a":1}
• •Arrays maintain order - [1,2,3] does NOT equal [3,2,1]
• •Comparison is deep and semantic, not string-based

Directory Structure

tests/
└── my-test-suite/
    ├── run                    # Executable (any language)
    └── data/
        └── scenario-name/
            ├── input.json     # Test input
            └── expected.json  # Expected output

The run Executable

The run file is any executable that:

1. •Reads JSON from stdin
2. •Writes JSON to stdout
3. •Exit code 0 = success, non-zero = error

Example (bash):

#!/usr/bin/env bash
jq '.value * 2'

Example (python):

#!/usr/bin/env python3
import json, sys
data = json.load(sys.stdin)
print(json.dumps({"result": data["value"] * 2}))

Pattern Matching

For dynamic values, use patterns in expected.json:

Example expected.json:

{
  "id": "<uuid>",
  "created_at": "<timestamp>",
  "count": "<number>"
}

Commands

tc                    # Run all tests in current directory
tc run path/to/suite  # Run specific suite
tc new path/to/suite  # Create new test suite scaffold
tc list               # List available test suites
tc tags               # Show available tags
tc explain suite      # Describe what a test does
tc --parallel         # Run tests in parallel
tc --tags=unit        # Filter by tag

Creating a New Test

tc new tests/user-creation

This creates:

tests/user-creation/
├── run
└── data/
    └── basic/
        ├── input.json
        └── expected.json

Best Practices

1. •One concept per test suite - each run tests one thing
2. •Multiple scenarios per suite - use data/ subdirectories for variations
3. •Descriptive scenario names - data/empty-input/, data/unicode-handling/
4. •Keep run minimal - just wire input to your code and format output
5. •Use patterns for non-deterministic values - timestamps, UUIDs, etc.

Why This Approach

• •Portable: Tests don't depend on any test framework or language
• •Diffable: JSON diffs are clear and human-readable
• •AI-friendly: Easy for AI to generate and verify tests
• •Implementation-agnostic: Rewrite in any language, tests still pass

Reference

• •Repository: https://github.com/ahoward/tc
• •Requires: bash 4.0+, jq