优化：按商户分组展示员工账号

backend/internal/service/merchant_test.go

@@ -256,6 +256,43 @@ func TestUserServicePromotesMerchantAccountToPlatformAdmin(t *testing.T) {
 	}
 }
 
+func TestListMerchantMembersGroupsEmployeesByMerchant(t *testing.T) {
+	db := newServiceTestDB(t)
+	merchantA := model.Merchant{Code: "grouped-members-a", Name: "分组商户 A", Status: model.MerchantStatusActive}
+	merchantB := model.Merchant{Code: "grouped-members-b", Name: "分组商户 B", Status: model.MerchantStatusActive}
+	employeeA := model.User{Username: "grouped-employee-a", PasswordHash: "hash", Role: model.RoleMerchant, Status: 1}
+	employeeB := model.User{Username: "grouped-employee-b", PasswordHash: "hash", Role: model.RoleMerchant, Status: 1}
+	admin := model.User{Username: "grouped-admin", PasswordHash: "hash", Role: model.RoleAdmin, Status: 1}
+	for _, entity := range []interface{}{&merchantA, &merchantB, &employeeA, &employeeB, &admin} {
+		if err := db.Create(entity).Error; err != nil {
+			t.Fatalf("create fixture: %v", err)
+		}
+	}
+	for _, member := range []model.MerchantMember{
+		{MerchantID: merchantA.ID, UserID: employeeA.ID, Role: model.MemberRoleOperator, Status: 1},
+		{MerchantID: merchantA.ID, UserID: employeeB.ID, Role: model.MemberRoleFinance, Status: 1},
+		{MerchantID: merchantB.ID, UserID: admin.ID, Role: model.MemberRoleOwner, Status: 1},
+	} {
+		if err := db.Create(&member).Error; err != nil {
+			t.Fatalf("create membership: %v", err)
+		}
+	}
+
+	groups, total, err := NewUserService(db, nil).ListMerchantMembers(1, 20)
+	if err != nil {
+		t.Fatalf("list grouped members: %v", err)
+	}
+	if total != 1 || len(groups) != 1 {
+		t.Fatalf("expected one merchant group, total=%d groups=%+v", total, groups)
+	}
+	if groups[0].MerchantID != merchantA.ID || groups[0].Merchant == nil || groups[0].Merchant.Name != merchantA.Name {
+		t.Fatalf("unexpected merchant group: %+v", groups[0])
+	}
+	if len(groups[0].Members) != 2 {
+		t.Fatalf("expected two employees in the merchant group, got %+v", groups[0].Members)
+	}
+}
+
 func TestEnsureAdminUsesConfiguredCredentialsOnlyForEmptyDatabase(t *testing.T) {
 	db := newServiceTestDB(t)
 	tenant := NewTenantService(db)