add(test)：添加单元测试

backend/IM_API/Models/ChatType.cs

@@ -0,0 +1,8 @@
+namespace IM_API.Models
+{
+    public enum ChatType
+    {
+        PRIVATE = 0,
+        GROUP = 1
+    }
+}

backend/IM_API/Models/ImContext.cs

@@ -49,10 +49,17 @@ public partial class ImContext : DbContext
     public virtual DbSet<Role> Roles { get; set; }
 
     public virtual DbSet<User> Users { get; set; }
-
     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
-#warning To protect potentially sensitive information in your connection string, you should move it out of source code. You can avoid scaffolding the connection string by using the Name= syntax to read it from configuration - see https://go.microsoft.com/fwlink/?linkid=2131148. For more guidance on storing connection strings, see https://go.microsoft.com/fwlink/?LinkId=723263.
-        => optionsBuilder.UseMySql("server=frp-era.com;port=26582;database=IM;user=product;password=12345678", Microsoft.EntityFrameworkCore.ServerVersion.Parse("5.7.44-mysql"));
+    {
+        if (!optionsBuilder.IsConfigured)
+        {
+            optionsBuilder.UseMySql(
+                "server=frp-era.com;port=26582;database=IM;user=product;password=12345678",
+                ServerVersion.Parse("5.7.44-mysql")
+            );
+        }
+    }
+
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {

backend/IM_API/Models/MessageExt.cs

@@ -7,6 +7,11 @@
             get => (MessageMsgType)MsgType;
             set => MsgType = (sbyte) value;
         }
+        public ChatType ChatTypeEnum
+        {
+            get => (ChatType)ChatType;
+            set => ChatType = (sbyte)value;
+        }
         public MessageState StateEnum
         {
             get => (MessageState)State;

backend/IM_API/Models/User.cs

@@ -20,7 +20,7 @@ public partial class User
     /// <summary>
     /// 用户昵称
     /// </summary>
-    public string NickName { get; set; } = null!;
+    public string? NickName { get; set; } = null!;
 
     /// <summary>
     /// 用户在线状态