Initialize CBDD solution and add a .NET-focused gitignore for generated artifacts.

tests/CBDD.Tests/ObjectIdTests.cs

@@ -0,0 +1,52 @@
+using ZB.MOM.WW.CBDD.Bson;
+using Xunit;
+
+namespace ZB.MOM.WW.CBDD.Tests;
+
+public class ObjectIdTests
+{
+    [Fact]
+    public void NewObjectId_ShouldCreate12ByteId()
+    {
+        var oid = ObjectId.NewObjectId();
+
+        Span<byte> bytes = stackalloc byte[12];
+        oid.WriteTo(bytes);
+
+        bytes.Length.ShouldBe(12);
+    }
+
+    [Fact]
+    public void ObjectId_ShouldRoundTrip()
+    {
+        var original = ObjectId.NewObjectId();
+
+        Span<byte> bytes = stackalloc byte[12];
+        original.WriteTo(bytes);
+
+        var restored = new ObjectId(bytes);
+
+        restored.ShouldBe(original);
+    }
+
+    [Fact]
+    public void ObjectId_Equals_ShouldWork()
+    {
+        var oid1 = ObjectId.NewObjectId();
+        var oid2 = oid1;
+        var oid3 = ObjectId.NewObjectId();
+
+        oid2.ShouldBe(oid1);
+        oid3.ShouldNotBe(oid1);
+    }
+
+    [Fact]
+    public void ObjectId_Timestamp_ShouldBeRecentUtc()
+    {
+        var oid = ObjectId.NewObjectId();
+        var timestamp = oid.Timestamp;
+
+        (timestamp <= DateTime.UtcNow).ShouldBeTrue();
+        (timestamp >= DateTime.UtcNow.AddSeconds(-5)).ShouldBeTrue();
+    }
+}