Add NWNX VM tests. Fix NWNX function name marshalling.

NWNX.NET.Tests/src/main/Tests/NWNXVMTests.cs

@@ -0,0 +1,26 @@
+using NUnit.Framework;
+
+namespace NWNX.NET.Tests
+{
+  [TestFixture(Category = "NWNX VM Tests")]
+  public sealed class NWNXVMTests
+  {
+    [Test]
+    [TestCase("NWNX_Core", 1)]
+    [TestCase("NWNX_DotNET", 1)]
+    [TestCase("NWNX_SWIG_DotNET", 1)]
+    [TestCase("NWNX_MissingPlugin", 0)]
+    [TestCase("", 0)]
+    [TestCase(null, 0, Ignore = "NWNX throws a std::logic_error")]
+    public void PluginExistsTest(string plugin, int expectedResult)
+    {
+      NWNXAPI.NWNXSetFunction("NWNX_Core", "PluginExists");
+      NWNXAPI.NWNXPushString(plugin);
+      NWNXAPI.NWNXCallFunction();
+
+      int result = NWNXAPI.NWNXPopInt();
+
+      Assert.That(result, Is.EqualTo(expectedResult));
+    }
+  }
+}

NWNX.NET/src/main/API/NWNXAPI.VM.NWNX.cs

@@ -15,7 +15,7 @@ public static partial class NWNXAPI
     /// <param name="function">The name of the function to call.</param>
     [LibraryImport("NWNX_DotNET", EntryPoint = "NWNXSetFunction")]
     [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
-    public static partial void NWNXSetFunction([MarshalUsing(typeof(Utf16StringMarshaller))] string plugin, [MarshalUsing(typeof(Utf16StringMarshaller))] string function);
+    public static partial void NWNXSetFunction([MarshalUsing(typeof(Utf8StringMarshaller))] string plugin, [MarshalUsing(typeof(Utf8StringMarshaller))] string function);
 
     /// <summary>
     /// NWNX VM Function. Push an integer to the current argument stack.