added field change and get and updated tests

src/db_get_user_by_id.c

@@ -1,9 +1,9 @@
-#include "user.h"
 #include "database.h"
 #include "sql.h"
+#include "user.h"
 
 User *db_get_user_by_id(const int id) {
-    User *user = nullptr;
+  User *user = nullptr;
   pthread_mutex_lock(&db_mutex);
   if (!db) {
     fprintf(stderr, "Database not initialized\n");
@@ -11,12 +11,11 @@ User *db_get_user_by_id(const int id) {
     return nullptr;
   }
   sqlite3_stmt *stmt;
-  int rc =
-      sqlite3_prepare_v2(db, SELECT_USER_BY_ID_SQL, -1, &stmt, nullptr);
+  int rc = sqlite3_prepare_v2(db, SELECT_USER_BY_ID_SQL, -1, &stmt, nullptr);
   if (rc != SQLITE_OK) {
     fprintf(stderr, "Cannot prepare statement: %s\n", sqlite3_errmsg(db));
-    sqlite3_close(db);
-    exit(1);
+    pthread_mutex_unlock(&db_mutex);
+    return nullptr;
   }
 
   sqlite3_bind_int(stmt, 1, id);
@@ -36,9 +35,10 @@ User *db_get_user_by_id(const int id) {
     fprintf(stderr, "Error reading data: %s\n", sqlite3_errmsg(db));
     free_user(user);
     sqlite3_finalize(stmt);
+    pthread_mutex_unlock(&db_mutex);
     return nullptr;
   }
 
   pthread_mutex_unlock(&db_mutex);
   return user;
-}
+}