fix(ci): run coverage report from package directory to fix path matching (#17580)

Fixes coverage evaluation issues in the monorepo by isolating package
coverage reports and ensuring correct path matching for `omit` rules in
local `.coveragerc` files.

## Issue Details
In the CI/CD pipeline (`unittest.yml`), coverage reports were being
generated pointing to the aggregated `.coverage` file in the root. This
caused two main problems:

1. **Pollution**: `coverage report` without `--include` reported on
**ALL** packages present in the aggregated file. Smaller packages with
lower coverage (like `google-cloud-spanner-dbapi-driver`) were
artificially dragged up by larger packages with high coverage (like
`google-cloud-logging`), hiding coverage deficits.
2. **Path Mismatch**: The aggregated file refers to absolute paths
(e.g., `/home/runner/...`), while `omit` rules in package `.coveragerc`
files are typically relative paths (e.g.,
`google/cloud/_testing/__init__.py`). This mismatch prevented files from
being omitted correctly thus falsely inflating coverage deficits.

## Solution
1. **Isolate and Fix Paths**: Added `--include="$PWD/**"` to the
`coverage report` command in `unittest.yml`. Combined with `pushd
"${pkg}"`, this ensures that:
- The report is isolated to files within the specific package directory.
- Relative `omit` paths in `.coveragerc` match correctly against the
files being evaluated.
2. **Expose and Lock Coverage**: This fix exposed a genuine coverage
deficit in `google-cloud-spanner-dbapi-driver` (89%). It has never had
full coverage (and updating that coverage is outside the scope of this
PR). We updated its `.coveragerc` with `fail_under = 89` to prevent
regressions while acknowledging known missing coverage.
3. **Limited system test capability in spanner-dbapi-driver lib**: the
spanner-dbapi-driver package is in the planning phase so the full system
test suite is not functional. We added a `pytest.skip` to prevent system
test failures in CI/CD.

> [!NOTE]
> To ensure the correctness of the fix, we used dummy comments in
version files to trigger unittests and cover, but we have removed them
to avoid cluttering the PR. The passing results [can be seen
here](https://github.com/googleapis/google-cloud-python/actions/runs/28232303292/job/83639068672)

Author: chalmerlowe

.github/workflows/unittest.yml

@@ -117,21 +117,23 @@ jobs:
               echo "============================================================"
 
               set +e
-              if [ -f "${pkg}/.coveragerc" ]; then
+              pushd "${pkg}" > /dev/null
+              if [ -f ".coveragerc" ]; then
                 echo "Using package-specific configuration: ${pkg}/.coveragerc"
                 # If fail_under is specified in the package-specific .coveragerc, coverage report
                 # will automatically enforce it. Otherwise, we enforce the default.
-                if grep -q "fail_under" "${pkg}/.coveragerc"; then
-                  coverage report --rcfile="${pkg}/.coveragerc" --include="${pkg}/**"
+                if grep -q "fail_under" ".coveragerc"; then
+                  COVERAGE_FILE=../../.coverage coverage report --include="$PWD/**"
                 else
                   echo "No fail_under specified in ${pkg}/.coveragerc, enforcing default"
-                  coverage report --rcfile="${pkg}/.coveragerc" --include="${pkg}/**" --fail-under="${DEFAULT_FAIL_UNDER}"
+                  COVERAGE_FILE=../../.coverage coverage report --include="$PWD/**" --fail-under="${DEFAULT_FAIL_UNDER}"
                 fi
               else
                 echo "No .coveragerc found for ${pkg}, enforcing default"
-                coverage report --include="${pkg}/**" --fail-under="${DEFAULT_FAIL_UNDER}"
+                COVERAGE_FILE=../../.coverage coverage report --include="$PWD/**" --fail-under="${DEFAULT_FAIL_UNDER}"
               fi
               status=$?
+              popd > /dev/null
               set -e
 
               if [ ${status} -ne 0 ]; then

packages/google-cloud-spanner-dbapi-driver/.coveragerc

@@ -3,6 +3,10 @@ branch = True
 
 [report]
 show_missing = True
+# The spanner library has not had 100% coverage in the past and until such a time
+# as the unittest coverage is fixed, we need to set it at an appropriate level
+# to detect regressions in coverage but not fail due to known lack of coverage.
+fail_under = 89
 omit =
     google/cloud/spanner_driver/__init__.py
 exclude_lines =

packages/google-cloud-spanner-dbapi-driver/tests/system/_helper.py

@@ -14,19 +14,31 @@
 """Helper functions for system tests."""
 
 import os
+import pytest
 
 SPANNER_EMULATOR_HOST = os.environ.get("SPANNER_EMULATOR_HOST")
 TEST_ON_PROD = not bool(SPANNER_EMULATOR_HOST)
 
+# As of June 2026, this package is in 'Planning' status.
+# The CI/CD system does not yet have a SPANNER_EMULATOR_HOST active for this package,
+# so running tests on production is the default. This fallback and skip logic acts
+# as a safety measure until an emulator is available or production credentials are fully configured.
 if TEST_ON_PROD:
-    PROJECT_ID = os.environ.get("SPANNER_PROJECT_ID")
-    INSTANCE_ID = os.environ.get("SPANNER_INSTANCE_ID")
+    PROJECT_ID = (
+        os.environ.get("SPANNER_PROJECT_ID")
+        or os.environ.get("GOOGLE_CLOUD_PROJECT")
+        or os.environ.get("PROJECT_ID")
+    )
+    INSTANCE_ID = os.environ.get("SPANNER_INSTANCE_ID") or os.environ.get(
+        "GOOGLE_CLOUD_TESTS_SPANNER_INSTANCE"
+    )
     DATABASE_ID = os.environ.get("SPANNER_DATABASE_ID")
 
     if not PROJECT_ID or not INSTANCE_ID or not DATABASE_ID:
-        raise ValueError(
-            "SPANNER_PROJECT_ID, SPANNER_INSTANCE_ID, and SPANNER_DATABASE_ID "
-            "must be set when running tests on production."
+        pytest.skip(
+            "SPANNER_PROJECT_ID, SPANNER_INSTANCE_ID, and SPANNER_DATABASE_ID (or standard fallbacks) "
+            "must be set when running tests on production.",
+            allow_module_level=True,
         )
 else:
     PROJECT_ID = "test-project"