chore: parallelize testing in ci with xdist

.github/actions/run-tests/action.yml

@@ -15,7 +15,7 @@ inputs:
   pytest-args:
     description: 'Additional arguments to pass to pytest'
     required: false
-    default: '--mpl -W error::metpy.deprecation.MetpyDeprecationWarning'
+    default: '--mpl -W error::metpy.deprecation.MetpyDeprecationWarning -n auto --cov --cov-report=xml'
 runs:
   using: composite
   steps:
@@ -30,10 +30,8 @@ runs:
       # By running coverage in "parallel" mode and "combining", we can clean up the path names
       run: |
         set -e -o pipefail
-        python -m coverage run -p -m pytest ${{ inputs.pytest-args }} tests/ 2>&1 | tee tests-${{ inputs.key }}.log
-        python -m coverage combine
-        python -m coverage report
-        python -m coverage xml
+        python -m pytest ${{ inputs.pytest-args }} tests/ 2>&1 | tee tests-${{ inputs.key }}.log
+
 
     - name: Run doctests
       if: ${{ inputs.run-doctests == 'true' }}

CONTRIBUTING.md

@@ -300,7 +300,14 @@ To run these tests, use:
 
 ```sh
 pytest --mpl
-````
+```
+
+To run tests in parallel, use `-n <number_of_processes>` or `-n auto` (using `pytest-xdist`):
+
+```sh
+pytest --mpl -n auto
+pytest --mpl -n 2
+```
 
 When adding new image comparison tests, start by creating the baseline images for the tests:
 

ci-dev/test_requirements.txt

@@ -1,5 +1,7 @@
 packaging==25.0
 pytest==8.4.0
+pytest-cov==6.2.1
 pytest-mpl==0.17.0
+pytest-xdist==3.8.0
 coverage==7.10.2
 vcrpy==7.0.0

pyproject.toml

@@ -58,6 +58,8 @@ test = [
     "netCDF4",
     "packaging>=21.0",
     "pytest>=7.0",
+    "pytest-xdist",
+    "pytest-cov",
     "pytest-mpl",
     "vcrpy>=4.3.1"
 ]