Compare to empty string when start script test fails
#!/bin/bash
set -euo pipefail
-if [ "$TEST_START_VAR" != "var is set" ]
+# set value of TEST_START_VAR to empty string when it is not defined
+if [ "${TEST_START_VAR:-}" != "var is set" ]
then
echo "TEST_START_VAR is not set"
exit 1
