address code review

Author: Takashi Matsuo

.kokoro/tests/run_tests.sh

@@ -21,26 +21,21 @@ shopt -s globstar
 
 DIFF_FROM=""
 
-# We need to temporarily turn off -e for detecting changes in the test
-# driver.
-set +e
-
 # `--only-diff-master` will only run tests on project changes on the
 # last common commit from the master branch.
 if [[ $* == *--only-diff-master* ]]; then
+    set +e
     git diff --quiet "origin/master..." .kokoro/tests .kokoro/docker \
 	.kokoro/trampoline_v2.sh
     CHANGED=$?
+    set -e
     if [[ "${CHANGED}" -eq 0 ]]; then
 	DIFF_FROM="origin/master..."
     else
 	echo "Changes to test driver files detected. Running full tests."
     fi
 fi
 
-# Turning on the -e again.
-set -e
-
 # `--only-diff-head` will only run tests on project changes from the
 # previous commit.
 if [[ $* == *--only-diff-head* ]]; then