In [Deno 1.4](https://deno.land/posts/v1.4) a new flag `--coverage` for `deno test` was added to collect test coverage. In [Deno 1.8](https://deno.land/posts/v1.8) support for lcov format was shipped, meaning that we can now easily setup coverage report services. In this tutorial I will show how to configure [Codecov](https://codecov.io) and [Github Actions](https://github.com/actions) for online coverage report. ## Writing tests Deno provides a convinient built-in API for writing tests. It also has a [special standard module](https://deno.land/std@0.89.0/testing) for testing that includes assertion functions and benchmarking. Let's write a simple test: ```ts // sum_test.ts import { assertEquals } from 'https://deno.land/std/testing/asserts.ts' import { sum } from './sum.ts' Deno.test({ name: 'sum(a + b)', fn: () => { assertEquals(sum(2, 3), 5) } }) ``` If you are used to Jest-like testing you might try [Wizard](https://github.com/deno-libs/wizard): ```ts // sum_test.ts import { sum } from './sum.ts' import { describe, it, expect, run } from 'https://deno.land/x/tincan/mod.ts' describe('A test suite', () => { it('should sum a + b', () => { expect(sum(2, 3)).toBe(5) }) }) run() // Start test runner ``` To run the test type this in the terminal: ```sh deno test ``` ## Generating coverage To produce the coverage files from tests you need to use `--coverage` and `--unstable` (because it is still an experimental feature) flags for the `deno test` command: ```sh deno test --coverage=coverage ``` This will create a set of coverage files in the `coverage` folder. You can pick any folder as the coverage output by specicyfing it with the `--coverage` flag. Next, we need to generate a coverage report so services like Codecov will be able to consume it: ```sh deno coverage ./coverage --lcov > coverage.lcov ``` After running the command a new file "coverage.lcov" will get created. We created the coverage locally but it doesn't get uploaded anywhere for now. ## Codecov For online coverage report we will use [Codecov](https://codecov.io/). Sign up there and open the URL with your repository address: ```url https://app.codecov.io/gh// ``` Later Codecov will know that this repo has been initiated before for coverage upload. ## GitHub Actions As the CI I'll be using GitHub Actions because it already has a premade [Deno action](https://github.com/denolib/setup-deno) and is easy to configure. The config looks something like this: ```yml name: CI # Controls when the action will run. Triggers the workflow on push or pull request # events but only for the master branch on: push: branches: [master] pull_request: branches: [master] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v2 - uses: denolib/setup-deno@v2 with: deno-version: v1.8 - name: Create coverage files run: deno test --unstable --coverage=coverage # create coverage files - name: Create coverage report run: deno --unstable coverage ./coverage --lcov > coverage.lcov # create coverage report - name: Collect coverage uses: codecov/codecov-action@v1.0.10 # upload the report on Codecov with: file: ./coverage.lcov ``` Create a file called `ci.yml` or `main.yml` with these contents and put it in the `.github/workflows` folder in your repository. This will trigger GitHub to use their CI. After pushing that file Github Actions will start running. Congrats! Now you have continious test run and coverage report. ## Badges For convinience you may also add badges as indicators: ```markdown [![](https://img.shields.io/github/workflow/status///CI?style=flat-square)](https://github.com///actions) [![](https://img.shields.io/codecov/c/gh//?style=flat-square)](https://codecov.io/gh//) ``` ## Useful Links * [Deno manual](https://deno.land/manual/testing#test-coverage) * [std/testing](https://deno.land/std@0.89.0/testing) ## Conclusion Despite that coverage tooling in Deno is relatively new, it's already possible to set the full toolchain up with no hassle. Notice that it's all done by the Deno CLI commands, unlike Node, where you have to (at least) install `c8` and `uvu` for tests and coverage report.

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