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hamzafarooqhamzafarooq/claude-code-starter/.claude/skills/test-writer/SKILL.md

test-writer

Skill145 starsChanged 6 months agoMITView on GitHub

Write unit tests for any function — happy path, edge cases, and error cases. Use when the user asks for tests, wants to add test coverage, or is practicing TDD.

We split this skill into the rules it gives an agent

3 rules. 0 are common, 3 are distinctive, and 0 are very specific to this project.

  • 0

    Common

    Most of the 27 edited versions we read keep these.

  • 3

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Ask the user to share the function or code they want tests for.

    line 6
  2. Distinctive:

    Test the expected behavior with valid inputs.

    line 17
  3. Distinctive:

    Write tests that read like documentation — the test name should be a sentence explaining what the function does in that scenario.

    line 47

“Common” is measured: kept by at least 6 in 10 of the 27 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Ask the user to share the function or code they want tests for.

Then write tests covering:

Tests for [functionName]

Testing framework: [detect from package.json — Jest, Vitest, pytest, etc. Ask if unclear]

Happy path

Test the expected behavior with valid inputs. One test per meaningful variation.

test('returns [expected] when given [input]', () => {
  // arrange
  // act
  // assert
})

Edge cases

Tests for boundary conditions and unusual but valid inputs:

  • Empty input (empty string, empty array, 0)
  • Single item
  • Maximum size or value
  • Special characters (if string input)

Error cases

Tests that verify the function fails correctly:

  • Invalid input types
  • Null/undefined inputs
  • Inputs that should trigger error handling

Mock requirements

List any external dependencies (API calls, database queries, file system) that need mocking, with example mock setup.

Coverage target: Aim for all branches, not just lines. Flag any branch that is difficult to test and explain why.

Write tests that read like documentation — the test name should be a sentence explaining what the function does in that scenario.

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