[Java.Interop-Tests] Add test for JniMarshalMethod return type handling.

I'm trying to migrate Java.Interop.Export to use JniEnvironment, and
hitting errors regarding System.Linq.Expressions use when methods have
non-`void` return types.

Since the Java.Interop.Export code is based in part on
JniMarshalMethod, add a test for a method with a non-`void` return
type for more sanity checking.

Author: jonpryor

src/Java.Interop/Tests/Java.Interop/JniMarshalMethodTests.cs

@@ -45,6 +45,34 @@ public void CreateMarshalMethodExpression ()
 }");
 		}
 
+		[Test]
+		public void CreateMarshalMethodExpression_GetStringValueHandler ()
+		{
+			var t = typeof (Func<IntPtr, IntPtr, int, IntPtr>);
+			var m = typeof (TestType).GetMethod ("GetStringValueHandler", BindingFlags.NonPublic | BindingFlags.Static);
+			var d = Delegate.CreateDelegate (t, m);
+			CheckCreateMarshalMethodExpression (d, t,
+					@"IntPtr (IntPtr arg1, IntPtr arg2, int arg3)
+{
+	JniEnvironment __envp;
+
+	__envp = new JniEnvironment(arg1);
+	try
+	{
+		return TestType.GetStringValueHandler(arg1, arg2, arg3);
+	}
+	catch (Exception __e)
+	{
+		__envp.SetPendingException(__e);
+		return default(IntPtr);
+	}
+	finally
+	{
+		__envp.Dispose();
+	}
+}");
+		}
+
 		static void CheckCreateMarshalMethodExpression (Delegate value, Type expectedDelegateType, string expectedBody)
 		{
 			var l   = JniMarshalMethod.CreateMarshalMethodExpression (value);

src/Java.Interop/Tests/Java.Interop/TestType.cs

@@ -18,7 +18,7 @@ static TestType ()
 			_members.JniPeerType.RegisterNativeMethods (
 					new JniNativeMethodRegistration ("equalsThis", "(Ljava/lang/Object;)Z", GetEqualsThisHandler ()),
 					new JniNativeMethodRegistration ("getInt32Value", "()I", GetInt32ValueHandler ()),
-					new JniNativeMethodRegistration ("getStringValue", "(I)Ljava/lang/String;", GetStringValueHandler ()),
+					new JniNativeMethodRegistration ("getStringValue", "(I)Ljava/lang/String;", _GetStringValueHandler ()),
 					new JniNativeMethodRegistration ("methodThrows", "()V", (Action<IntPtr, IntPtr>) MethodThrowsHandler));
 		}
 
@@ -111,21 +111,24 @@ static Delegate GetInt32ValueHandler ()
 			return h;
 		}
 
-		static Delegate GetStringValueHandler ()
+		static Delegate _GetStringValueHandler ()
 		{
-			Func<IntPtr, IntPtr, int, IntPtr> h = (jnienv, n_self, value) => {
-				var self = JniEnvironment.Current.JavaVM.GetObject<TestType>(n_self);
-				try {
-					var s = self.GetStringValue (value);
-					using (var r = JniEnvironment.Strings.NewString (s))
-						return JniEnvironment.Handles.NewReturnToJniRef (r);
-				} finally {
-					self.DisposeUnlessRegistered ();
-				}
-			};
+			Func<IntPtr, IntPtr, int, IntPtr> h = GetStringValueHandler;
 			return h;
 		}
 
+		static IntPtr GetStringValueHandler (IntPtr jnienv, IntPtr n_self, int value)
+		{
+			var self = JniEnvironment.Current.JavaVM.GetObject<TestType>(n_self);
+			try {
+				var s = self.GetStringValue (value);
+				using (var r = JniEnvironment.Strings.NewString (s))
+					return JniEnvironment.Handles.NewReturnToJniRef (r);
+			} finally {
+				self.DisposeUnlessRegistered ();
+			}
+		}
+
 		static void MethodThrowsHandler (IntPtr jnienv, IntPtr n_self)
 		{
 			var self = JniEnvironment.Current.JavaVM.GetObject<TestType> (n_self);