diff --git a/source/MongoDB.Tests/MongoDB.Tests.csproj b/source/MongoDB.Tests/MongoDB.Tests.csproj
index 4b21942d..0f1cfe25 100644
--- a/source/MongoDB.Tests/MongoDB.Tests.csproj
+++ b/source/MongoDB.Tests/MongoDB.Tests.csproj
@@ -95,7 +95,7 @@
     <Compile Include="UnitTests\Bson\BsonTestBase.cs" />
     <Compile Include="UnitTests\Bson\TestBsonBinary.cs" />
     <Compile Include="UnitTests\Bson\TestRoundTrips.cs" />
-    <Compile Include="UnitTests\Configuration\MongoConfigurationTests.cs" />
+    <Compile Include="UnitTests\Configuration\MongoConfigurationBuilderTests.cs" />
     <Compile Include="IntegrationTests\Connections\TestConnection.cs" />
     <Compile Include="IntegrationTests\Connections\TestConnectionFactory.cs" />
     <Compile Include="IntegrationTests\Connections\TestPooledConnectionFactory.cs" />
@@ -104,6 +104,7 @@
     <Compile Include="IntegrationTests\Linq\LinqTestsBase.cs" />
     <Compile Include="IntegrationTests\Linq\MongoQueryTests.cs" />
     <Compile Include="IntegrationTests\Linq\MongoQueryProviderTests.cs" />
+    <Compile Include="UnitTests\Configuration\MongoConfigurationTests.cs" />
     <Compile Include="UnitTests\Serialization\Builders\DocumentPropertyTests.cs" />
     <Compile Include="UnitTests\Serialization\Builders\EmbeddedClassPropertyTests.cs" />
     <Compile Include="UnitTests\Serialization\Builders\EnumerablePropertyTests.cs" />
diff --git a/source/MongoDB.Tests/UnitTests/Configuration/MongoConfigurationTests.cs b/source/MongoDB.Tests/UnitTests/Configuration/MongoConfigurationTests.cs
new file mode 100644
index 00000000..eef4372a
--- /dev/null
+++ b/source/MongoDB.Tests/UnitTests/Configuration/MongoConfigurationTests.cs
@@ -0,0 +1,61 @@
+using System;
+using MongoDB.Configuration;
+using NUnit.Framework;
+
+namespace MongoDB.UnitTests.Configuration
+{
+    [TestFixture]
+    public class MongoConfigurationTests
+    {
+        [Test]
+        public void IsModifiableByDefault()
+        {
+            var config = new MongoConfiguration();
+            Assert.IsTrue(config.IsModifiable);
+        }
+
+        [Test]
+        public void IsNotModifiableAfterValidate()
+        {
+            var config = new MongoConfiguration();
+            config.ValidateAndSeal();
+            Assert.IsFalse(config.IsModifiable);            
+        }
+
+        [Test]    
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void CanNotChangeConnectionStringAfterValidate()
+        {
+            var config = new MongoConfiguration();
+            config.ValidateAndSeal();
+            config.ConnectionString = "";
+        }
+
+        [Test]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void CanNotChangeMappingStoreAfterValidate()
+        {
+            var config = new MongoConfiguration();
+            config.ValidateAndSeal();
+            config.MappingStore = null;
+        }
+
+        [Test]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void CanNotChangeReadLocalTimeAfterValidate()
+        {
+            var config = new MongoConfiguration();
+            config.ValidateAndSeal();
+            config.ReadLocalTime = true;
+        }
+
+        [Test]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void CanNotChangeSerializationFactoryAfterValidate()
+        {
+            var config = new MongoConfiguration();
+            config.ValidateAndSeal();
+            config.SerializationFactory = null;
+        }
+    }
+}
\ No newline at end of file