test(head-and-tail): check if the submitted file is correct and check if echo is used

sh/tests/head-and-tail_test.sh

@@ -5,12 +5,24 @@ set -euo pipefail
 IFS='
 '
 
-echo insecure >> ~/.curlrc
-caddy start &>/dev/null
+FILENAME="student/head-and-tail.sh"
 
-submitted=$(bash student/head-and-tail.sh)
+# True if FILE exists and is a regular file
+if [ -f ${FILENAME} ]; then
+    # FILE exists and it's not empty
+    if [ -s ${FILENAME} ]; then
+        if [[ $(cat $FILENAME | grep echo | wc -l) -ne 0 ]]; then
+            echo "echo is not allowed in this exercise!";
+            exit 1
+        fi
+        submitted=$(bash $FILENAME)
         expected=$(bash solutions/head-and-tail.sh)
-
-caddy stop &>/dev/null
-
         diff <(echo "$submitted") <(echo "$expected")
+    else
+        echo "The file exist but is empty"
+        exit 1
+    fi
+else
+    echo "File does not exist"
+    exit 1
+fi