diff --git a/.github/workflows/python-publish.yml b/.github/workflows/python-publish.yml
index c5f6ac1..1aa91b3 100644
--- a/.github/workflows/python-publish.yml
+++ b/.github/workflows/python-publish.yml
@@ -6,21 +6,21 @@ name: Upload Python Package
 on:
   push: {}
   release:
-    types: [created]
+    types: [ created ]
 
 jobs:
   quality:
     name: Code QA
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - run: pip install black flake8 isort
-      - run: black --version
-      - run: isort --version
-      - run: flake8 --version
-      - run: isort --check .
-      - run: black --check .
-      - run: flake8 .
+    - uses: actions/checkout@v2
+    - run: pip install black flake8 isort
+    - run: black --version
+    - run: isort --version
+    - run: flake8 --version
+    - run: isort --check .
+    - run: black --check .
+    - run: flake8 .
 
   checks:
     if: ${{ github.event_name == 'release' }}
@@ -28,29 +28,29 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        platform: ["ubuntu-latest", "macos-latest"]
-        python-version: ["3.9", "3.10", "3.11" ]
+        platform: [ "ubuntu-latest", "macos-latest" ]
+        python-version: [ "3.9", "3.10", "3.11" ]
 
     name: Python  ${{ matrix.python-version }} on ${{ matrix.platform }}
     runs-on: ${{ matrix.platform }}
     needs: quality
 
     steps:
-      - uses: actions/checkout@v2
+    - uses: actions/checkout@v2
 
-      - uses: actions/setup-python@v2
-        with:
-          python-version: ${{ matrix.python-version }}
+    - uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
 
-      - name: Install
-        run: |
-          pip install pytest
-          pip install -e .
-          pip install -r tests/requirements.txt
-          pip freeze
+    - name: Install
+      run: |
+        pip install pytest
+        pip install -e .
+        pip install -r tests/requirements.txt
+        pip freeze
 
-      - name: Tests
-        run: pytest
+    - name: Tests
+      run: env SOURCES_TO_TEST=ecmwf pytest
 
   deploy:
 
@@ -68,11 +68,11 @@ jobs:
 
     - name: Check that tag version matches code version
       run: |
-          tag=${GITHUB_REF#refs/tags/}
-          version=$(python setup.py --version)
-          echo 'tag='$tag
-          echo "version file="$version
-          test "$tag" == "$version"
+        tag=${GITHUB_REF#refs/tags/}
+        version=$(python setup.py --version)
+        echo 'tag='$tag
+        echo "version file="$version
+        test "$tag" == "$version"
 
     - name: Install dependencies
       run: |
diff --git a/tests/test_sources.py b/tests/test_sources.py
index c98aba3..0b305bc 100644
--- a/tests/test_sources.py
+++ b/tests/test_sources.py
@@ -1,10 +1,11 @@
 import pytest
+import os
 
 from ecmwf.opendata import Client
 from ecmwf.opendata.bufr import count_bufrs
 from ecmwf.opendata.grib import count_gribs
 
-SOURCES = ["ecmwf", "azure", "aws"]
+SOURCES = os.getenv("SOURCES_TO_TEST", "ecmwf,azure,aws").split(",")
 
 
 @pytest.mark.parametrize("source", SOURCES)