fixes bug: setting user who is not present in pianist-table is no longer allowed

rep_cli.py

@@ -23,9 +23,19 @@ class Session:
                         }
 
     def set_user(self, arguments):
+        resultstring = ''
         db_index = arguments[0]
-        self.user = db_index
-        return 'User set'
+        sql_command = f'''
+                      SELECT *
+                      FROM pianist
+                      WHERE id = {db_index}
+                      '''
+        if self.db_agent.execute(sql_command).fetchone():
+            self.user = db_index
+            resultstring += 'User set'
+        else:
+            resultstring += 'No such user' 
+        return resultstring
 
     def get_active_user(self):
         sql_command = f'''