diff --git a/Tests/Cosmos.Compiler.Tests.Bcl/Cosmos.Compiler.Tests.Bcl.csproj b/Tests/Cosmos.Compiler.Tests.Bcl/Cosmos.Compiler.Tests.Bcl.csproj
index 392913276..2cdfd269f 100644
--- a/Tests/Cosmos.Compiler.Tests.Bcl/Cosmos.Compiler.Tests.Bcl.csproj
+++ b/Tests/Cosmos.Compiler.Tests.Bcl/Cosmos.Compiler.Tests.Bcl.csproj
@@ -80,6 +80,7 @@
   <ItemGroup>
     <Compile Include="Kernel.cs" />
     <Compile Include="AssemblyInfo.cs" />
+    <Compile Include="System\BitConverterTest.cs" />
     <Compile Include="System\BooleanTest.cs" />
     <Compile Include="System\ByteTest.cs" />
     <Compile Include="System\CharTest.cs" />
diff --git a/Tests/Cosmos.Compiler.Tests.Bcl/Kernel.cs b/Tests/Cosmos.Compiler.Tests.Bcl/Kernel.cs
index 7a774cd65..3545b6501 100644
--- a/Tests/Cosmos.Compiler.Tests.Bcl/Kernel.cs
+++ b/Tests/Cosmos.Compiler.Tests.Bcl/Kernel.cs
@@ -36,6 +36,7 @@ namespace Cosmos.Compiler.Tests.Bcl
                 CharTest.Execute();
                 BooleanTest.Execute();
                 SingleTest.Execute();
+                BitConverterTest.Execute();
                 DoubleTest.Execute();
                 DecimalTest.Execute();
                 System.Collections.Generic.ListTest.Execute();
diff --git a/Tests/Cosmos.Compiler.Tests.Bcl/System/BitConverterTest.cs b/Tests/Cosmos.Compiler.Tests.Bcl/System/BitConverterTest.cs
new file mode 100644
index 000000000..9ce3c4da9
--- /dev/null
+++ b/Tests/Cosmos.Compiler.Tests.Bcl/System/BitConverterTest.cs
@@ -0,0 +1,65 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Cosmos.TestRunner;
+
+namespace Cosmos.Compiler.Tests.Bcl.System
+{
+    class BitConverterTest
+    {
+        public static void Execute()
+        {
+            String result;
+            String expectedResult;
+
+            int anInt = 1;
+
+            byte[] intBytes = BitConverter.GetBytes(anInt);
+
+            result = BitConverter.ToString(intBytes, 0);
+            expectedResult = "01-00-00-00";
+
+            Assert.IsTrue((result == expectedResult), "BitConverter.ToString(intBytes) doesn't work: result " + result + " != " + expectedResult);
+
+            long aLong = 1;
+
+            byte[] longBytes = BitConverter.GetBytes(aLong);
+
+            result = BitConverter.ToString(longBytes, 0);
+            expectedResult = "01-00-00-00-00-00-00-00";
+
+            Assert.IsTrue((result == expectedResult), "BitConverter.ToString(longBytes) doesn't work: result " + result + " != " + expectedResult);
+
+            ulong anULong = 1;
+
+            byte[] ulongBytes = BitConverter.GetBytes(anULong);
+
+            result = BitConverter.ToString(ulongBytes, 0);
+            expectedResult = "01-00-00-00-00-00-00-00";
+
+            Assert.IsTrue((result == expectedResult), "BitConverter.ToString(ulongBytes) doesn't work: result " + result + " != " + expectedResult);
+
+            // These tests fails bytes are screwed!
+
+            float aFloat = 1.0f;
+
+            byte[] floatBytes = BitConverter.GetBytes(aFloat);
+
+            result = BitConverter.ToString(floatBytes, 0);
+            expectedResult = "00-00-80-3F";
+
+            Assert.IsTrue((result == expectedResult), "BitConverter.ToString(floatBytes) doesn't work: result " + result + " != " + expectedResult);
+
+            double aDouble = 1.0;
+
+            byte[] doubleBytes = BitConverter.GetBytes(aDouble);
+
+            result = BitConverter.ToString(doubleBytes, 0);
+            expectedResult = "00-00-00-00-00-00-F0-3F";
+
+            Assert.IsTrue((result == expectedResult), "BitConverter.ToString(doubleBytes) doesn't work: result " + result + " != " + expectedResult);
+
+
+        }
+    }
+}
diff --git a/Tests/Cosmos.Compiler.Tests.Bcl/System/Int64Test.cs b/Tests/Cosmos.Compiler.Tests.Bcl/System/Int64Test.cs
index e71c18728..0a9538e6c 100644
--- a/Tests/Cosmos.Compiler.Tests.Bcl/System/Int64Test.cs
+++ b/Tests/Cosmos.Compiler.Tests.Bcl/System/Int64Test.cs
@@ -37,7 +37,13 @@ namespace Cosmos.Compiler.Tests.Bcl.System
             // actually the Hash Code of a Int64 is the value interpolated with XOR to obtain an Int32... so not the same of 'value'!
             int expectedResultAsInt = (unchecked((int)((long)value)) ^ (int)(value >> 32));
   
-            Assert.IsTrue((resultAsInt == expectedResultAsInt), "Int64.GetHashCode() doesn't work"); // XXX TODO when GetHashCode() works
+            Assert.IsTrue((resultAsInt == expectedResultAsInt), "Int64.GetHashCode() doesn't work"); 
+
+            // Let's try to convert a Long in a ULong
+            Int64 val2 = 42;
+            UInt64 val2AsULong = (ulong)val2;
+
+            Assert.IsTrue((val2AsULong == 42), "Int64 to UInt64 conversion does not work");
 
 #if false
             // Now let's try ToString() again but printed in hex (this test fails for now!)
diff --git a/Tests/Cosmos.Compiler.Tests.Bcl/System/UInt64Test.cs b/Tests/Cosmos.Compiler.Tests.Bcl/System/UInt64Test.cs
index 65040b55c..f793917fc 100644
--- a/Tests/Cosmos.Compiler.Tests.Bcl/System/UInt64Test.cs
+++ b/Tests/Cosmos.Compiler.Tests.Bcl/System/UInt64Test.cs
@@ -40,7 +40,13 @@ namespace Cosmos.Compiler.Tests.Bcl.System
             // actually the Hash Code of a Int64 is the value interpolated with XOR to obtain an Int32... so not the same of 'value'!
             int expectedResultAsInt = ((int)value) ^ (int)(value >> 32);
 
-            Assert.IsTrue((resultAsInt == expectedResultAsInt), "UInt64.GetHashCode() doesn't work"); // XXX TODO when GetHashCode() works
+            Assert.IsTrue((resultAsInt == expectedResultAsInt), "UInt64.GetHashCode() doesn't work");
+
+            // Let's try to convert an ULong in a Long
+            UInt64 val2 = 42;
+            Int64 val2AsLong = (long)val2;
+
+            Assert.IsTrue((val2AsLong == 42), "UInt64 to Int64 conversion does not work");
 
 #if false
             // Now let's try ToString() again but printed in hex (this test fails for now!)