Fixed issue with signed enum constants with tests.

src/AST/Enumeration.cs

@@ -56,10 +56,11 @@ namespace CppSharp.AST
 
         public string GetItemValueAsString(Item item)
         {
-            var format = item.IsHexadecimal ? "x" : string.Empty;
+            var printAsHex = item.IsHexadecimal && BuiltinType.IsUnsigned;
+            var format = printAsHex ? "x" : string.Empty;
             var value = BuiltinType.IsUnsigned ? item.Value.ToString(format) :
                 ((long)item.Value).ToString(format);
-            return item.IsHexadecimal ? "0x" + value : value;
+            return printAsHex ? "0x" + value : value;
         }
 
         public Enumeration SetFlags()

tests/Basic/Basic.Tests.cs

@@ -38,6 +38,9 @@ public class BasicTests
         Assert.That(hello.RetEnum(Enum.A), Is.EqualTo(0));
         Assert.That(hello.RetEnum(Enum.B), Is.EqualTo(2));
         Assert.That(hello.RetEnum(Enum.C), Is.EqualTo(5));
+        Assert.That(hello.RetEnum(Enum.D), Is.EqualTo(-2147483648));
+        Assert.That(hello.RetEnum(Enum.E), Is.EqualTo(1));
+        Assert.That(hello.RetEnum(Enum.F), Is.EqualTo(-9));
     }
 
     static void Main(string[] args)

tests/Basic/Basic.h

@@ -34,7 +34,10 @@ struct DLL_API Bar2 : public Bar
 
 enum Enum
 {
-    A = 0, B = 2, C = 5
+    A = 0, B = 2, C = 5,
+    Signed = 0x80000000,
+    F = 0x1,
+    H = -9
 };
 
 class DLL_API Hello
@@ -57,4 +60,4 @@ public:
     int AddBar2(Bar2);
 
     int RetEnum(Enum);
-};
+};