Add failing test to reproduce #859

Test/Mono.Cecil.Tests/ImageWriteTests.cs

@@ -0,0 +1,48 @@
+using System.IO;
+using System.Linq;
+using NUnit.Framework;
+
+#if NETCOREAPP
+
+namespace Mono.Cecil.Tests {
+	[TestFixture]
+	public class ImageWriteTests : BaseTestFixture {
+
+		[TestCase("EmbeddedPdbTarget.exe")]
+		// [TestCase("ExternalPdbDeterministic.dll")]
+		public void MultipleWriteOperationsShouldReturnSameOutput (string testee)
+		{
+			TestModule (testee, module => {
+				Assert.IsTrue (module.HasDebugHeader);
+
+				const int numberOfStreams = 5;
+
+				MemoryStream Write(int _)
+				{
+					var stream = new MemoryStream ();
+					module.Write (stream, new WriterParameters { WriteSymbols = true });
+					return stream;
+				}
+
+				var streams = Enumerable.Range (0, numberOfStreams)
+					.Select (Write)
+					.ToArray ();
+
+				static bool AreStreamsEqual ((MemoryStream First, MemoryStream Second) pair)
+				{
+					var buffer1 = pair.First.GetBuffer ();
+					var buffer2 = pair.Second.GetBuffer ();
+					return buffer1.SequenceEqual (buffer2);
+				}
+
+				var results = streams.Zip (streams.Skip (1))
+					.Select (AreStreamsEqual)
+					.ToArray ();
+
+				Assert.That (results, Is.EquivalentTo (results.Select (_ => true)));
+			});
+		}
+	}
+}
+
+#endif