Add test for TypeHelper and improve ReflectionHelper

framework/src/Volo.Abp.Core/Volo/Abp/Reflection/ReflectionHelper.cs

@@ -53,14 +53,14 @@ namespace Volo.Abp.Reflection
 
             if (givenTypeInfo.IsGenericType && givenType.GetGenericTypeDefinition() == genericType)
             {
-                result.Add(givenType);
+                result.AddIfNotContains(givenType);
             }
 
             foreach (var interfaceType in givenTypeInfo.GetInterfaces())
             {
                 if (interfaceType.GetTypeInfo().IsGenericType && interfaceType.GetGenericTypeDefinition() == genericType)
                 {
-                    result.Add(interfaceType);
+                    result.AddIfNotContains(interfaceType);
                 }
             }
 

framework/test/Volo.Abp.Core.Tests/Volo/Abp/Reflection/TypeHelper_Tests.cs

@@ -16,6 +16,27 @@ namespace Volo.Abp.Reflection
             guidType.ShouldBe(typeof(Guid));
         }
 
+        [Fact]
+        public void IsEnumerable()
+        {
+            TypeHelper.IsEnumerable(
+                typeof(IEnumerable<string>),
+                out var itemType
+            ).ShouldBeTrue();
+            itemType.ShouldBe(typeof(string));
+
+            TypeHelper.IsEnumerable(
+                typeof(List<TypeHelper_Tests>),
+                out itemType
+            ).ShouldBeTrue();
+            itemType.ShouldBe(typeof(TypeHelper_Tests));
+
+            TypeHelper.IsEnumerable(
+                typeof(TypeHelper_Tests),
+                out itemType
+            ).ShouldBeFalse();
+        }
+
         [Fact]
         public void IsDictionary()
         {