Add tests calling function imports.

crates/misc/dotnet/tests/FunctionThunkingTests.cs

@@ -0,0 +1,71 @@
+using FluentAssertions;
+using System;
+using System.Linq;
+using Xunit;
+
+namespace Wasmtime.Tests
+{
+    public class FunctionThunkingFixture : ModuleFixture
+    {
+        protected override string ModuleFileName => "FunctionThunking.wasm";
+    }
+
+    public class FunctionThunkingTests : IClassFixture<FunctionThunkingFixture>
+    {
+        const string THROW_MESSAGE = "Test error messages for wasmtime dotnet bidnings unit tests.";
+
+        class MyHost : IHost
+        {
+            public Instance Instance { get; set; }
+
+            [Import("add", Module = "env")]
+            public int Add(int x, int y) => x + y;
+
+            [Import("do_throw", Module = "env")]
+            public void Throw() => throw new Exception(THROW_MESSAGE);
+        }
+
+        public FunctionThunkingTests(FunctionThunkingFixture fixture)
+        {
+            Fixture = fixture;
+        }
+
+        private FunctionThunkingFixture Fixture { get; }
+
+        [Fact]
+        public void ItBindsImportMethodsAndCallsThemCorrectly()
+        {
+            var host = new MyHost();
+            using (var instance = Fixture.Module.Instantiate(host))
+            {
+                var add_func = instance.Externs.Functions.Where(f => f.Name == "add_wrapper").Single();
+                int invoke_add(int x, int y) => (int)add_func.Invoke(new object[] { x, y });
+
+                invoke_add(40, 2).Should().Be(42);
+                invoke_add(22, 5).Should().Be(27);
+
+                //Collect garbage to make sure delegate function pointers pasted to wasmtime are rooted.
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+
+                invoke_add(1970, 50).Should().Be(2020);
+            }
+        }
+
+        [Fact]
+        public void ItPropegatesExceptionsToCallersViaTraps()
+        {
+            var host = new MyHost();
+            using (var instance = Fixture.Module.Instantiate(host))
+            {
+                var throw_func = instance.Externs.Functions.Where(f => f.Name == "do_throw_wrapper").Single();
+                Action action = () => throw_func.Invoke();
+
+                action
+                    .Should()
+                    .Throw<TrapException>()
+                    .WithMessage(THROW_MESSAGE);
+            }
+        }
+    }
+}