C# Error: Error CS0246 The type or namespace name '' could not be found (are you missing a using directive or an assembly reference?)

I have an application which suppports both UWP and .NET. I have a namespace test which is .net specific. So I have included it conditional like

#if! WINDOWS_UWP
using test;
#endif

test contain classes mytest,mytest1,mytest2. But only one is showing up when I tried test dot .

#if! WINDOWS_UWP
mytest obj = new mytest()
#endif

showing error :"Error CS0246 The type or namespace name '' could not be found (are you missing a using directive or an assembly reference?)"

When I tried the same in a sample .net application, all classes are showing up when I used test dot. test comes from a nuget package.

Please help.

Thanks,