build: reduce build time

.github/workflows/presubmit.yaml

@@ -0,0 +1,41 @@
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+name: Presubmit checks
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: 3.8
+      - name: Install nox
+        run: python -m pip install nox
+      - name: Check formatting
+        run: nox -s lint
+      - name: Check lint setup
+        run: nox -s lint_setup_py
+  units:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python: [3.8, 3.9, 3.10, 3.11, 3.12, 3.13]
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{matrix.python}}
+      - name: Install nox
+        run: python -m pip install nox
+      - name: Run unit tests
+        run: nox -s unit-${{matrix.python}}

.kokoro/presubmit/presubmit.cfg

@@ -5,3 +5,8 @@ env_vars: {
     key: "RUN_SYSTEM_TESTS"
     value: "false"
 }
+# Only run a subset of all nox sessions
+env_vars: {
+    key: "NOX_SESSION"
+    value: "unit-3.8 unit-3.12 cover docs docfx"
+}

noxfile.py

@@ -329,9 +329,12 @@ def system(session, protobuf_implementation, database_dialect):
         session.skip(
             "Credentials or emulator host must be set via environment variable"
         )
-    # If POSTGRESQL tests and Emulator, skip the tests
-    if os.environ.get("SPANNER_EMULATOR_HOST") and database_dialect == "POSTGRESQL":
-        session.skip("Postgresql is not supported by Emulator yet.")
+    if not (
+        os.environ.get("SPANNER_EMULATOR_HOST") or protobuf_implementation == "python"
+    ):
+        session.skip(
+            "Only run system tests on real Spanner with one protobuf implementation to speed up the build"
+        )
 
     # Install pyopenssl for mTLS testing.
     if os.environ.get("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true":