diff --git a/Sources/Model/Dice/DiceGroupManager.cs b/Sources/Model/Dice/DiceGroupManager.cs
index 1d0ccc5..9efbbb5 100644
--- a/Sources/Model/Dice/DiceGroupManager.cs
+++ b/Sources/Model/Dice/DiceGroupManager.cs
@@ -23,6 +23,21 @@ namespace Model.Dice
             }
             diceGroups.Add(new(toAdd.Name.Trim(), toAdd.Dice));
             return Task.FromResult(toAdd);
+        }
+
+        public Task<DiceGroup> AddCheckName(DiceGroup toAdd)
+        {
+            if (string.IsNullOrWhiteSpace(toAdd.Name))
+            {
+                throw new ArgumentNullException(nameof(toAdd), "param should not be null or empty");
+
+            }
+            if (diceGroups.Where(d => d.Name.Equals(toAdd.Name)).Any())
+            {
+                throw new ArgumentException("this dice group already exists", nameof(toAdd));
+            }
+            diceGroups.Add(new(toAdd.Name.Trim(), toAdd.Dice));
+            return Task.FromResult(toAdd);
         }
 
         public Task<ReadOnlyCollection<DiceGroup>> GetAll()
diff --git a/Sources/Tests/Data_UTs/Dice/DiceGroupManagerTest.cs b/Sources/Tests/Data_UTs/Dice/DiceGroupManagerTest.cs
index b0fe4a3..7b7c87e 100644
--- a/Sources/Tests/Data_UTs/Dice/DiceGroupManagerTest.cs
+++ b/Sources/Tests/Data_UTs/Dice/DiceGroupManagerTest.cs
@@ -1,22 +1,22 @@
-using Data;
-using Data.EF;
-using Microsoft.Data.Sqlite;
-using Microsoft.EntityFrameworkCore;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using Model.Dice;
-using Model.Dice.Faces;
-using Model.Games;
-using System;
-using System.Collections.Generic;
-using System.Collections.ObjectModel;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using Xunit;
-
-namespace Tests.Data_UTs.Dice
-{
-    public class DiceGroupManagerTest
+using Data;
+using Data.EF;
+using Microsoft.Data.Sqlite;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Model.Dice;
+using Model.Dice.Faces;
+using Model.Games;
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Tests.Data_UTs.Dice
+{
+    public class DiceGroupManagerTest
     {
         private static readonly Task<MasterOfCeremonies> stubGameRunner = new Stub().LoadApp();
         [Fact]
@@ -43,18 +43,18 @@ namespace Tests.Data_UTs.Dice
         public async Task TestAddWhenDiceGroupThenDoAddAndReturnDiceGroup()
         {
             // Arrange
-            DiceGroupManager dgm = new();
-            DiceGroup group1 = new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) });
+            DiceGroupManager dgm = new();
+            DiceGroup group1 = new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) });
             DiceGroup group2 = new("Scrabble", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) });
 
             //...storing the results of DiceGroupManager.Add() in variables 
-            Collection<DiceGroup> expected = new() {group1,group2 };
-            Collection<DiceGroup> actual = new()
-            {
-                await dgm.Add(group1),
-                await dgm.Add(group2)
-            };
-            // Assert
+            Collection<DiceGroup> expected = new() {group1,group2 };
+            Collection<DiceGroup> actual = new()
+            {
+                await dgm.Add(group1),
+                await dgm.Add(group2)
+            };
+            // Assert
             Xunit.Assert.Equal(expected, actual);
             Xunit.Assert.Equal(expected, actual);
         }
@@ -68,8 +68,8 @@ namespace Tests.Data_UTs.Dice
             async Task actionAsync() => await dgm.Add(expected);// Add() returns the added element if succesful
 
             // Assert
-            Xunit.Assert.Null(expected);
-            await Xunit.Assert.ThrowsAsync<ArgumentNullException>(actionAsync);
+            Xunit.Assert.Null(expected);
+            await Xunit.Assert.ThrowsAsync<ArgumentNullException>(actionAsync);
             Xunit.Assert.DoesNotContain(expected, await dgm.GetAll());
         }
         [Fact]
@@ -77,13 +77,13 @@ namespace Tests.Data_UTs.Dice
         {
             DiceGroupManager dgm = new();
 
-            await dgm.Add(new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) }));
+            await dgm.AddCheckName(new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) }));
             DiceGroup group1 = new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) });
 
-            async Task actionAsync() => await dgm.Add(group1);
+            async Task actionAsync() => await dgm.AddCheckName(group1);
 
             // Assert
-            await Xunit.Assert.ThrowsAsync<Exception>(actionAsync);
+            await Xunit.Assert.ThrowsAsync<ArgumentException>(actionAsync);
 
         }
 
@@ -112,7 +112,7 @@ namespace Tests.Data_UTs.Dice
             DiceGroup toAdd = new("Monopoly", new List<NumberDie> { new NumberDie(new NumberFace(5), new NumberFace(7)), new NumberDie(new NumberFace(5), new NumberFace(7)) });
             
             await dgm.Add(toAdd);
-            async Task action() => dgm.GetOneByName(name);
+            async Task action() => await dgm.GetOneByName(name);
 
             // Assert
            await Xunit.Assert.ThrowsAsync<ArgumentNullException>(action);
@@ -237,5 +237,5 @@ namespace Tests.Data_UTs.Dice
 
 
 
-    }
-}
+    }
+}