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How to use the Kotlin Testing Patterns agent skill (kotlin-testing)

Updated · written with AI from the project's own documentation and checked against our catalogue data

The kotlin-testing skill is a set of Kotlin testing reference patterns that an AI coding agent reads when it writes or reviews tests. It covers Kotest spec styles, MockK mocking, coroutine testing, property-based testing and Kover coverage, following a test-first workflow. This guide shows you how to install it, how to ask for it in plain language, and what your project needs before it is useful.

Kotlin Testing Patternsaffaan-m/ECC · MIT

Quick start

  1. 1Download and unzip. Download the skill ZIP from this page and unzip it so you have a kotlin-testing folder containing SKILL.md.
  2. 2Place the folder. Move the folder into ~/.claude/skills/ for all projects, or into your project's .claude/skills/ folder for one project.
  3. 3Check your build. Confirm your project is built with Gradle and has Kotest, MockK and Kover added.
  4. 4Ask in plain language. Describe the Kotlin testing task, for example writing Kotest tests for a service with MockK mocks.
  5. 5Follow the test-first cycle. Ask the agent to write a failing test, run ./gradlew test, implement the minimal code, and refactor.
  6. 6Check coverage. Run ./gradlew koverHtmlReport and review the report against the 80% target in the skill.

What does the kotlin-testing skill make the agent do?

When the skill is installed, the agent follows structured Kotlin testing practices. It picks a Kotest spec style that fits the test scope, mocks dependencies with MockK so the unit under test is isolated, and works test-first: write a failing test, make it pass with minimal code, then refactor.

It also checks coverage with Kover. The skill's workflow ends with running ./gradlew koverHtmlReport and verifying 80% or more coverage. The file is mostly reference examples, so the agent tends to produce more idiomatic Kotlin tests than it would without it.

  • Kotest styles covered: StringSpec, FunSpec, BehaviorSpec and DescribeSpec
  • MockK setup, coroutine mocking and argument capture
  • Kotest matchers such as shouldBe, shouldContain and shouldThrow
  • Ktor testApplication examples for testing routes

How do you install the kotlin-testing skill?

Download the ZIP for the skill from this page and unzip it. The skill is a folder containing a SKILL.md file. Place that folder in one of these locations:

  • Personal (all projects): ~/.claude/skills/
  • Single project: the .claude/skills/ folder inside your project
  • Claude apps: upload the ZIP under Settings → Capabilities → Skills

How do you trigger the skill with natural requests?

You do not need a special command. Describe the testing task in plain language that mentions Kotlin, and the agent should pick up the skill when the request matches its description. The skill's description covers Kotest, MockK, coroutine testing, property-based testing, Kover and TDD.

Requests that fit well include writing tests for a new function, adding coverage to existing code, or working test-first on a new feature.

  • "Write Kotest tests for this OrderService using MockK for the repository."
  • "Follow TDD to add an email validator in Kotlin. Start with failing tests."
  • "Set up Kover and show me how to generate an HTML coverage report."
  • "Add testApplication tests for my Ktor login route."

What examples does the skill include?

The TDD walkthrough builds a validateEmail function in steps: a stub that throws NotImplementedError, a StringSpec test file, a run that shows the failures, a minimal implementation, and a second run that passes. A BehaviorSpec example shows Given/When/Then tests for placing an order, with coVerify checking that payment was charged once.

Other examples show a FunSpec service test that mocks a repository with coEvery, and a DescribeSpec validator test grouped by context.

./gradlew test ./gradlew koverHtmlReport

What does your project need?

The skill assumes a Kotlin project built with Gradle, since the commands it references are ./gradlew test and koverHtmlReport. The Kotest, MockK and Kover libraries need to be added to your build. If you test Ktor routes, the Ktor testApplication library is also needed.

The patterns assume Kotest and MockK. If your project uses JUnit-only or Java testing, the examples will need adapting.

  • A Kotlin project built with Gradle
  • Kotest, MockK and Kover added to the build
  • Ktor testApplication library, only if testing Ktor routes

What are the safety notes?

According to the listing, this skill does not run scripts and does not use the network. The file is SKILL.md, a reference document. The commands it shows, such as ./gradlew test, are run by you or the agent in your own project, so review what the agent runs as you would for any build command.

Tips for getting better results

Name the spec style you want, such as BehaviorSpec for Given/When/Then, so the agent does not have to guess. Tell the agent which mocking library and build tool you use. Ask for the RED step explicitly if you want to see the test fail before the code exists.

  • State the scope: unit test, service test or route test
  • Ask for coverage numbers from koverHtmlReport after tests pass
  • Give the agent your existing test folder so it matches your naming

What people use it for

  • Writing Kotest unit tests for a service with mocked repositories
  • Driving a new Kotlin function test-first from failing tests to passing code
  • Adding Kover coverage reporting to an existing Gradle project
  • Writing Ktor testApplication tests for API routes
  • Writing property-based tests alongside example-based tests

Frequently asked questions

How do I install the kotlin-testing skill?

Download the ZIP from this page and unzip it. Put the kotlin-testing folder in ~/.claude/skills/ for all projects, or in a project's .claude/skills/ folder. In the Claude apps, you can upload the ZIP under Settings → Capabilities → Skills.

Is the kotlin-testing skill free?

The listing states the skill is licensed under MIT. Check the license terms on the source repository before you reuse or redistribute it.

What does my Kotlin project need to use it?

You need a Kotlin project built with Gradle, with Kotest, MockK and Kover added to the build. If you test Ktor routes, you also need the Ktor testApplication library.

Does it work with JUnit instead of Kotest?

Not well. The patterns assume Kotest and MockK, so JUnit-only or Java testing stacks would need the examples adapted.

Does the skill run scripts or use the internet?

According to the listing, it runs no scripts and uses no network. It is a SKILL.md reference file.

How is this different from just asking the agent to write tests?

The skill gives the agent a consistent set of Kotest, MockK, TDD and Kover practices with worked examples, so output tends to follow the same idiomatic patterns instead of varying from request to request.

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Our verdict

Choose this skill if you write Kotlin with Gradle and want tests in Kotest and MockK style, especially with test-driven development or Kover coverage. Pick something else if your project uses JUnit-only or Java testing, or if you are not comfortable running Gradle builds.

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