Add ThatDeriveFrom() extension method

Author: kevinkuszyk

src/FluentAssertions.Ioc.Ninject.Tests/FluentAssertions.Ioc.Ninject.Tests.csproj

@@ -60,6 +60,7 @@
   <ItemGroup>
     <Compile Include="KernelAssertionTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="TypeExtensionTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="app.config" />

src/FluentAssertions.Ioc.Ninject.Tests/TypeExtensionTests.cs

@@ -0,0 +1,25 @@
+using NUnit.Framework;
+
+namespace FluentAssertions.Ioc.Ninject.Tests
+{
+    [TestFixture]
+    public class TypeExtensionTests
+    {
+        [Test]
+        public void ThatDerivesFrom_returns_expected_types()
+        {
+            // Arrange
+            var expected = new [] { typeof(Bar) };
+            
+            // Act
+            var actual = FindAssembly.Containing<Foo>().GetTypes().ThatDeriveFrom<Foo>();
+
+            // Assert
+            actual.ShouldBeEquivalentTo(expected);
+        }
+    }
+
+    public class Foo { }
+
+    public class Bar : Foo { }
+}

src/FluentAssertions.Ioc.Ninject/TypeExtensions.cs

@@ -35,5 +35,15 @@ public static IEnumerable<Type> EndingWith(this IEnumerable<Type> types, string
         {
             return types.Where(x => x.Name.EndsWith(endingWith));
         }
+
+        /// <summary>
+        /// Filters to only include types which are derived from TBase.
+        /// </summary>
+        /// <typeparam name="TBase">The base class filtered types should derive from.</typeparam>
+        /// <param name="types">The types to filer.</param>
+        public static IEnumerable<Type> ThatDeriveFrom<TBase>(this IEnumerable<Type> types)
+        {
+            return types.Where(x => x.IsSubclassOf(typeof (TBase)));
+        }
     }
 }