The result of custom implementation of CreateInvalidItem is being che…

…ck so it doesn't return a key equals to valid key.

src/Thinktecture.Runtime.Extensions.SourceGenerator/CodeAnalysis/EnumSourceGenerator.cs

@@ -558,6 +558,14 @@ private void GenerateGet(bool needCreateInvalidImplementation)
             _sb.Append(@"
             if (item.IsValid)
                throw new Exception(""The implementation of method 'CreateInvalidItem' must return an instance with property 'IsValid' equals to 'false'."");");
+
+            if (!needCreateInvalidImplementation)
+            {
+               _sb.Append($@"
+
+            if ({_state.EnumType}.TryGet(item.{_state.KeyPropertyName}, out _))
+               throw new Exception(""The implementation of method 'CreateInvalidItem' must not return an instance with property '{_state.KeyPropertyName}' equals to one of a valid item."");");
+            }
          }
          else
          {

test/Thinktecture.Runtime.Extensions.SourceGenerator.Tests/SourceGeneratorTests/EnumSourceGeneratorTests.cs

@@ -1877,6 +1877,9 @@ string IEnum<string>.GetKey()
 
             if (item.IsValid)
                throw new Exception(""The implementation of method 'CreateInvalidItem' must return an instance with property 'IsValid' equals to 'false'."");
+
+            if (Thinktecture.Tests.TestEnum.TryGet(item.Name, out _))
+               throw new Exception(""The implementation of method 'CreateInvalidItem' must not return an instance with property 'Name' equals to one of a valid item."");
          }
 
          return item;

test/Thinktecture.Runtime.Extensions.Tests.Shared/TestEnums/TestEnumWithInvalidCreateInvalidItem.cs

@@ -0,0 +1,21 @@
+namespace Thinktecture.Runtime.Tests.TestEnums
+{
+   public partial class TestEnumWithInvalidCreateInvalidItem : IValidatableEnum<int>
+   {
+      public const int INVALID_KEY_FOR_TESTING_KEY_REUSE = 0;
+      public const int INVALID_KEY_FOR_TESTING_ISVALID_TRUE = -1;
+
+      public static readonly TestEnumWithInvalidCreateInvalidItem Item1 = new(1);
+
+      private static TestEnumWithInvalidCreateInvalidItem CreateInvalidItem(int key)
+      {
+         if (key == INVALID_KEY_FOR_TESTING_KEY_REUSE)
+            return new(Item1.Key, false);
+
+         if (key == INVALID_KEY_FOR_TESTING_ISVALID_TRUE)
+            return new(key, true);
+
+         return new(key, false);
+      }
+   }
+}

test/Thinktecture.Runtime.Extensions.Tests/EnumTests/Get.cs

@@ -58,6 +58,20 @@ public void Should_return_invalid_item_if_enum_doesnt_have_item_with_provided_ke
          extendedItem.Key.Should().Be("unknown");
       }
 
+      [Fact]
+      public void Should_throw_if_CreateInvalidItem_uses_key_of_valid_item()
+      {
+         Action action = () => TestEnumWithInvalidCreateInvalidItem.Get(TestEnumWithInvalidCreateInvalidItem.INVALID_KEY_FOR_TESTING_KEY_REUSE);
+         action.Should().Throw<Exception>().WithMessage("The implementation of method 'CreateInvalidItem' must not return an instance with property 'Key' equals to one of a valid item.");
+      }
+
+      [Fact]
+      public void Should_throw_if_CreateInvalidItem_isValid_is_true()
+      {
+         Action action = () => TestEnumWithInvalidCreateInvalidItem.Get(TestEnumWithInvalidCreateInvalidItem.INVALID_KEY_FOR_TESTING_ISVALID_TRUE);
+         action.Should().Throw<Exception>().WithMessage("The implementation of method 'CreateInvalidItem' must return an instance with property 'IsValid' equals to 'false'.");
+      }
+
       [Fact]
       public void Should_throw_if_custom_validation_throws()
       {