Create testing skill

Summary

Create a skill for writing and running tests in the omnirepo.

Skill Content

---
name: testing
description: Write and run tests for Haskell and Python code. Use when adding tests, verifying behavior, or debugging test failures.
---

# Testing

## Running Tests

\`\`\`bash
bild --test Omni/Task.hs    # Build and run tests
_/bin/task test             # Run tests on existing binary
\`\`\`

## Test Convention

All programs follow the pattern: if first arg is `test`, run tests.

\`\`\`haskell
main :: IO ()
main = do
  args <- getArgs
  case args of
    ["test"] -> runTests
    _ -> normalMain
\`\`\`

## Writing Tests (Haskell)

Use HUnit or similar:

\`\`\`haskell
runTests :: IO ()
runTests = do
  results <- runTestTT $ TestList
    [ "parse valid input" ~: parseInput "foo" ~?= Right Foo
    , "parse invalid input" ~: parseInput "" ~?= Left "empty"
    ]
  when (failures results > 0) exitFailure
\`\`\`

## Writing Tests (Python)

Use pytest:

\`\`\`python
# : dep pytest

def test_parse_valid():
    assert parse_input("foo") == Foo()

def test_parse_invalid():
    with pytest.raises(ValueError):
        parse_input("")
\`\`\`

## What to Test

- **Happy path** - Does it work with normal input?
- **Edge cases** - Empty, None, max values, boundaries
- **Error cases** - Invalid input, missing data, failures
- **Regressions** - Add test for each bug fix

## Test-Driven Debugging

When something breaks:
1. Write a test that reproduces the bug
2. Verify test fails
3. Fix the code
4. Verify test passes
5. Keep the test

## Test Coverage

Focus on:
- Public API functions
- Complex logic with branches
- Error handling paths
- Integration points

Don't over-test:
- Simple getters/setters
- Obvious wrappers
- Implementation details

Deliverables

• [ ] Omni/Ide/Test.md
• [ ] Include examples from actual omnirepo tests