enable unit tests via github action

Author: ohmayr

.github/workflows/unittest.yml

@@ -0,0 +1,61 @@
+on:
+  pull_request:
+    branches:
+      - main
+name: unittest
+jobs:
+  unit:
+    # TODO(https://github.com/googleapis/gapic-generator-python/issues/2303): use `ubuntu-latest` once this bug is fixed.
+    # Use ubuntu-22.04 until Python 3.7 is removed from the test matrix
+    # https://docs.github.com/en/actions/using-github-hosted-runners/using-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories
+    runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        python: {{unit_test_python_versions}}
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ '{{' }} matrix.python {{ '}}' }}
+    - name: Install nox
+      run: |
+        python -m pip install --upgrade setuptools pip wheel
+        python -m pip install nox
+    - name: Run unit tests
+      env:
+        COVERAGE_FILE: .coverage-${{ '{{' }} matrix.python {{ '}}' }}
+      run: |
+        nox -s unit-${{ '{{' }} matrix.python {{ '}}' }}
+    - name: Upload coverage results
+      uses: actions/upload-artifact@v4
+      with:
+        name: coverage-artifact-${{ '{{' }} matrix.python {{ '}}' }}
+        path: .coverage-${{ '{{' }} matrix.python {{ '}}' }}
+        include-hidden-files: true
+
+  cover:
+    runs-on: ubuntu-latest
+    needs:
+        - unit
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: "{{ default_python_version }}"
+    - name: Install coverage
+      run: |
+        python -m pip install --upgrade setuptools pip wheel
+        python -m pip install coverage
+    - name: Download coverage results
+      uses: actions/download-artifact@v4
+      with:
+        path: .coverage-results/
+    - name: Report coverage results
+      run: |
+        find .coverage-results -type f -name '*.zip' -exec unzip {} \;
+        coverage combine .coverage-results/**/.coverage*
+        coverage report --show-missing --fail-under={{ cov_level if cov_level != None else 100 }}