Add tools support to sampling (#976)

tests/ModelContextProtocol.Tests/Protocol/ToolChoiceTests.cs

@@ -0,0 +1,30 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+public class ToolChoiceTests
+{
+    [Fact]
+    public void DefaultModeIsNull()
+    {
+        Assert.Null(new ToolChoice().Mode);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("none")]
+    [InlineData("required")]
+    [InlineData("auto")]
+    [InlineData("something_custom")]
+    public void SerializesWithMode(string? mode)
+    {
+        ToolChoice toolChoice = new() { Mode = mode };
+
+        var json = JsonSerializer.Serialize(toolChoice, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<ToolChoice>(json, McpJsonUtilities.DefaultOptions);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal(mode, deserialized.Mode);
+    }
+}