Add documentation on matrix build, only upload coverage once

When testing in a matrix, uploads often fail after the first one. I’m testing against different versions of Python, and I only need to upload the coverage information once, by including

if: matrix.python-version == 3.8

in the codecov job. It took me a while to figure this out, so maybe it is nice to include this in the readme.

[zhuanyan-wang]

Multiple Node.js and multiple OS

Expand on what @jhidding and @rfgamaral have said. If you are testing on multiple Node.js versions and multiple OS at the same time, something like this will work:

strategy:
  matrix:
    os: [ubuntu-latest, windows-latest, macos-latest]
    node-version: [10.x, 12.x, 14.x]

runs-on: ${{ matrix.os }}

steps:
  - name: Post Coverage
    uses: codecov/codecov-action@v1
    if: matrix.os == 'ubuntu-latest' && matrix.node-version == '10.x'

This posts the coverage reports to Codecov, only when the OS is ubuntu-latest and the Node.js version is 10.x. Just change if: matrix.os == 'ubuntu-latest' && matrix.node-version == '10.x' based on your own setup.

Result

The Post Coverage is skipped when the OS or the Node.js version does not match:

Two subdirectories Default and Container have posted their reports once only (otherwise there will be 12 builds here):

[rfgamaral]

I’ve started using Codecov with GitHub Actions (on this test project for now) and I’m wondering what’s the best practice for matrix builds!?

This particular project tests the code against 3 different Node.js version and with my current workflow I’m uploading 3 different coverage reports (but they are always the same):

This doesn’t make much sense to me. Ideally, only one coverage report would be uploaded.

Now, I understand I can add an if statement to the upload step like @jhidding mentioned in the original post, but somehow that feels like a hacky solution.

What is the recommended best practice to upload the coverage report only once independently of the number of jobs due to matrix configurations in GitHub actions?