chore(python): conditionally load credentials in .kokoro/build.sh (#2137)

Source-Link: googleapis/synthtool@aa69fb7
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:f016446d6e520e5fb552c45b110cba3f217bffdd3d06bdddd076e9e6d13266cf

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,5 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:04c35dc5f49f0f503a306397d6d043685f8d2bb822ab515818c4208d7fb2db3a
-# created: 2025-01-16T15:24:11.364245182Z
+  digest: sha256:f016446d6e520e5fb552c45b110cba3f217bffdd3d06bdddd076e9e6d13266cf
+# created: 2025-02-21T19:32:52.01306189Z

.kokoro/build.sh

@@ -15,11 +15,13 @@
 
 set -eo pipefail
 
+CURRENT_DIR=$(dirname "${BASH_SOURCE[0]}")
+
 if [[ -z "${PROJECT_ROOT:-}" ]]; then
-    PROJECT_ROOT="github/python-bigquery"
+  PROJECT_ROOT=$(realpath "${CURRENT_DIR}/..")
 fi
 
-cd "${PROJECT_ROOT}"
+pushd "${PROJECT_ROOT}"
 
 # Disable buffering, so that the logs stream through.
 export PYTHONUNBUFFERED=1
@@ -28,10 +30,16 @@ export PYTHONUNBUFFERED=1
 env | grep KOKORO
 
 # Setup service account credentials.
-export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
+if [[ -f "${KOKORO_GFILE_DIR}/service-account.json" ]]
+then
+  export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
+fi
 
 # Setup project id.
-export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
+if [[ -f "${KOKORO_GFILE_DIR}/project-id.json" ]]
+then
+  export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
+fi
 
 # If this is a continuous build, send the test log to the FlakyBot.
 # See https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot.
@@ -46,7 +54,7 @@ fi
 # If NOX_SESSION is set, it only runs the specified session,
 # otherwise run all the sessions.
 if [[ -n "${NOX_SESSION:-}" ]]; then
-    python3 -m nox -s ${NOX_SESSION:-}
+  python3 -m nox -s ${NOX_SESSION:-}
 else
-    python3 -m nox
+  python3 -m nox
 fi