Added type NonGenericCollectionWrapper.cs in FluentAssertions/Common.…

… This ensures that the Count property is passed through to the underlying implementation, and also allows code that knows about it to directly access the wrapped collection object.

Updated AssertionExtensions.c to use NonGenericCollectionWrapper instead of System.Linq's .Cast<TItem> to produce the generic collections for use with GenericCollectionAssertions<TItem> in Should overloads for DataTableCollection, DataColumnCollection and DataRowCollection.
Updated the ContainTableWithName methods in DataTableCollectionAssertionExtensions.cs and ContainColumnWithName in DataColumnCollectionAssertionExtensions.cs to check if the assertion subject is a NonGenericCollectionWrapper and, if so, use it to gain access to the underlying Contains functionality rather than requiring the collection to be enumerated.

Src/FluentAssertions/AssertionExtensions.cs

@@ -391,7 +391,8 @@ public static StringCollectionAssertions Should(this IEnumerable<string> @this)
         [Pure]
         public static GenericCollectionAssertions<DataTable> Should(this DataTableCollection actualValue)
         {
-            return new GenericCollectionAssertions<DataTable>(actualValue.Cast<DataTable>());
+            return new GenericCollectionAssertions<DataTable>(
+                new NonGenericCollectionWrapper<DataTableCollection, DataTable>(actualValue));
         }
 
         /// <summary>
@@ -400,7 +401,8 @@ public static GenericCollectionAssertions<DataTable> Should(this DataTableCollec
         [Pure]
         public static GenericCollectionAssertions<DataColumn> Should(this DataColumnCollection actualValue)
         {
-            return new GenericCollectionAssertions<DataColumn>(actualValue.Cast<DataColumn>());
+            return new GenericCollectionAssertions<DataColumn>(
+                new NonGenericCollectionWrapper<DataColumnCollection, DataColumn>(actualValue));
         }
 
         /// <summary>
@@ -409,7 +411,8 @@ public static GenericCollectionAssertions<DataColumn> Should(this DataColumnColl
         [Pure]
         public static GenericCollectionAssertions<DataRow> Should(this DataRowCollection actualValue)
         {
-            return new GenericCollectionAssertions<DataRow>(actualValue.Cast<DataRow>());
+            return new GenericCollectionAssertions<DataRow>(
+                new NonGenericCollectionWrapper<DataRowCollection, DataRow>(actualValue));
         }
 
         /// <summary>

Src/FluentAssertions/Common/NonGenericCollectionWrapper.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace FluentAssertions.Common
+{
+    internal class NonGenericCollectionWrapper<TCollection, TItem> : ICollection<TItem>, IEnumerable<TItem>
+        where TCollection : ICollection, IEnumerable
+    {
+        public TCollection UnderlyingCollection { get; private set; }
+
+        public NonGenericCollectionWrapper(TCollection collection)
+        {
+            UnderlyingCollection = collection;
+        }
+
+        public int Count => UnderlyingCollection.Count;
+
+        public bool IsReadOnly => true;
+
+        public IEnumerator<TItem> GetEnumerator() => UnderlyingCollection.Cast<TItem>().GetEnumerator();
+
+        IEnumerator IEnumerable.GetEnumerator() => UnderlyingCollection.GetEnumerator();
+
+        public bool Contains(TItem item) => UnderlyingCollection.Cast<TItem>().Contains(item);
+
+        public void CopyTo(TItem[] array, int arrayIndex) => UnderlyingCollection.CopyTo(array, arrayIndex);
+
+        // Mutation is not supported, but these methods must be implemented to satisfy ICollection<T>:
+        // * Add
+        // * Clear
+        // * Remove
+
+        public void Add(TItem item) => throw new NotSupportedException();
+
+        public void Clear() => throw new NotSupportedException();
+
+        public bool Remove(TItem item) => throw new NotSupportedException();
+    }
+}

Src/FluentAssertions/Data/Extensions/DataColumnCollectionAssertionExtensions.cs

@@ -114,7 +114,18 @@ public static class DataColumnCollectionAssertionExtensions
                         assertion.Subject);
             }
 
-            if (!assertion.Subject.Any(column => column.ColumnName == expectedColumnName))
+            bool containsColumn;
+
+            if (assertion.Subject is NonGenericCollectionWrapper<DataColumnCollection, DataColumn> wrapper)
+            {
+                containsColumn = wrapper.UnderlyingCollection.Contains(expectedColumnName);
+            }
+            else
+            {
+                containsColumn = assertion.Subject.Any(column => column.ColumnName == expectedColumnName);
+            }
+
+            if (!containsColumn)
             {
                 Execute.Assertion
                     .BecauseOf(because, becauseArgs)
@@ -150,7 +161,18 @@ public static class DataColumnCollectionAssertionExtensions
                         assertion.Subject);
             }
 
-            if (assertion.Subject.Any(column => column.ColumnName == unexpectedColumnName))
+            bool containsColumn;
+
+            if (assertion.Subject is NonGenericCollectionWrapper<DataColumnCollection, DataColumn> wrapper)
+            {
+                containsColumn = wrapper.UnderlyingCollection.Contains(unexpectedColumnName);
+            }
+            else
+            {
+                containsColumn = assertion.Subject.Any(column => column.ColumnName == unexpectedColumnName);
+            }
+
+            if (containsColumn)
             {
                 Execute.Assertion
                     .BecauseOf(because, becauseArgs)

Src/FluentAssertions/Data/Extensions/DataTableCollectionAssertionExtensions.cs

@@ -101,7 +101,18 @@ public static class DataTableCollectionAssertionExtensions
                         assertion.Subject);
             }
 
-            if (!assertion.Subject.Any(table => table.TableName == expectedTableName))
+            bool containsTable;
+
+            if (assertion.Subject is NonGenericCollectionWrapper<DataTableCollection, DataTable> wrapper)
+            {
+                containsTable = wrapper.UnderlyingCollection.Contains(expectedTableName);
+            }
+            else
+            {
+                containsTable = assertion.Subject.Any(table => table.TableName == expectedTableName);
+            }
+
+            if (!containsTable)
             {
                 Execute.Assertion
                     .BecauseOf(because, becauseArgs)
@@ -137,7 +148,18 @@ public static class DataTableCollectionAssertionExtensions
                         assertion.Subject);
             }
 
-            if (assertion.Subject.Any(table => table.TableName == unexpectedTableName))
+            bool containsTable;
+
+            if (assertion.Subject is NonGenericCollectionWrapper<DataTableCollection, DataTable> wrapper)
+            {
+                containsTable = wrapper.UnderlyingCollection.Contains(unexpectedTableName);
+            }
+            else
+            {
+                containsTable = assertion.Subject.Any(table => table.TableName == unexpectedTableName);
+            }
+
+            if (containsTable)
             {
                 Execute.Assertion
                     .BecauseOf(because, becauseArgs)