Update commit format test to work locally

Set default values for the remote name and
base branch when the test is run locally and
the Buildkite variables are not available and
the variables BASE_BRANCH and REMOTE are not set.

Signed-off-by: Catalin Dumitru <catdum@amazon.com>

integration_tests/test_commit_format.py

@@ -1,6 +1,14 @@
 # Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 # SPDX-License-Identifier: Apache-2.0
-"""Test the commit message format."""
+"""
+Test the commit message format.
+
+This test works properly on the local machine only when the environment
+variables BASE_BRANCH and REMOTE are set. Otherwise the default values
+are "master" for the name of the base branch and "origin" for the
+remote name of the upstream repository, and this test may not work as
+expected.
+"""
 
 import os
 import subprocess
@@ -9,8 +17,14 @@ from utils import get_cmd_output
 
 COMMIT_TITLE_MAX_LEN = 50
 COMMIT_BODY_LINE_MAX_LEN = 72
-BASE_BRANCH = os.environ['BUILDKITE_PULL_REQUEST_BASE_BRANCH']
-BASE_REPO = os.environ['BUILDKITE_REPO']
+BASE_BRANCH = \
+    os.environ.get('BUILDKITE_PULL_REQUEST_BASE_BRANCH') or \
+    os.environ.get('BASE_BRANCH') or \
+    "master"
+REMOTE = \
+    os.environ.get('BUILDKITE_REPO') or \
+    os.environ.get('REMOTE') or \
+    "origin"
 
 
 def test_commit_format():
@@ -22,8 +36,14 @@ def test_commit_format():
     and if commits are signed.
     """
     # Fetch the upstream repository.
-    fetch_base_cmd = "git fetch {} {}".format(BASE_REPO, BASE_BRANCH)
-    subprocess.run(fetch_base_cmd, shell=True, check=True)
+    fetch_base_cmd = "git fetch {} {}".format(REMOTE, BASE_BRANCH)
+    try:
+        subprocess.run(fetch_base_cmd, shell=True, check=True)
+    except subprocess.CalledProcessError:
+        raise NameError(
+            "The name of the base branch or remote is invalid. "
+            "See test documentation for more details."
+        ) from None
     # Get hashes of PR's commits in their abbreviated form for
     # a prettier printing.
     shas_cmd = "git log --no-merges --pretty=%h --no-decorate " \