fix exit on cd failure and unit test

.github/workflows/bashtest.yml

@@ -15,4 +15,7 @@ jobs:
 
     - name: Lint Bash scripts
       run: |
-        find . -name "*.sh" -print0 | xargs -0 shellcheck
+        find . -name "*.sh" -print0 | xargs -0 shellcheck -f gcc | tee shellcheck.log
+        if grep -q "error:" shellcheck.log; then
+          exit 1
+        fi

setup.sh

@@ -25,7 +25,8 @@ if [[ ! -d "$LINUXTOOLBOXDIR/mybash" ]]; then
     fi
 fi
 
-cd "$LINUXTOOLBOXDIR/mybash"
+
+cd "$LINUXTOOLBOXDIR/mybash" || exit
 
 command_exists() {
     command -v $1 >/dev/null 2>&1