CSHARP-4377: Flush on read-only stream should be a NOP. (#971)

Author: JamesKovacs

src/MongoDB.Driver.GridFS/GridFSDownloadStreamBase.cs

@@ -100,12 +100,13 @@ public override void Close(CancellationToken cancellationToken)
 
         public override void Flush()
         {
-            throw new NotSupportedException();
+            // CSHARP-4377: Flush on read-only stream should be a NOP
         }
 
         public override Task FlushAsync(CancellationToken cancellationToken)
         {
-            throw new NotSupportedException();
+            // CSHARP-4377: Flush on read-only stream should be a NOP
+            return Task.CompletedTask;
         }
 
         public override void SetLength(long value)

tests/MongoDB.Driver.GridFS.Tests/GridFSDownloadStreamBaseTests.cs

@@ -220,7 +220,7 @@ public void FileInfo_should_return_expected_result()
 
         [Theory]
         [ParameterAttributeData]
-        public void Flush_should_throw(
+        public void Flush_should_not_throw(
             [Values(false, true)] bool async)
         {
             var bucket = CreateBucket(128);
@@ -238,7 +238,7 @@ public void Flush_should_throw(
                 action = () => subject.Flush();
             }
 
-            action.ShouldThrow<NotSupportedException>();
+            action.ShouldNotThrow<NotSupportedException>();
         }
 
         [Fact]