ci: Allow for single exercise test exection

bin/test.sh

@@ -13,6 +13,17 @@ file_ext="php"
 function main {
   has_failures=0
 
+  if [ $# -ge 1 ] && [ -n "$1" ]; then
+    specific_exercise=$(find ./exercises/{practice,concept} -name $1 -type d | sort)
+    for exercise_dir in $specific_exercise; do
+        test "${exercise_dir}" "example"
+        if [[ $? -ne 0 ]]; then
+          has_failures=1
+        fi
+      done
+      return $has_failures
+  fi
+
   all_practice_exercise_dirs=$(find ./exercises/practice -maxdepth 1 -mindepth 1 -type d | sort)
   for exercise_dir in $all_practice_exercise_dirs; do
     test "${exercise_dir}" "example"