How i can create a very big stream for imititate big file?

Question

I am working on a multi-threaded archiver and at the moment I am thinking about how I can create a unit test that will send a very large stream to the class, instead of keeping the test files for compression. Is it possible? That my program.cs

 using (var sourceStream = new FileStream(args[1], FileMode.Open, FileAccess.Read))
                using (var destinationStream = new FileStream(args[2], FileMode.Create, FileAccess.Write))
                {
                    AbstractArchiver archiver;
                    switch (args[0])
                    {
                        case "compress":
                            archiver = new Compress(sourceStream, destinationStream);
                            archiver.Run();
                            break;
                        case "decompress":
                            archiver = new Decompress(sourceStream, destinationStream);
                            archiver.Run();
                            break;
                    }
                }