Added iteration upgrading for streams

Encrypter Tests/EncrypterTests.cs

@@ -168,6 +168,81 @@ namespace Encrypter_Tests
             }
         }
 
+        [Test]
+        public async Task TestUpgradedIterationsBehaviourStreaming()
+        {
+            var tempFileInput = Path.GetTempFileName();
+            var tempFileEncryptedPrevious = Path.GetTempFileName();
+            var tempFileReEncrypted = Path.GetTempFileName();
+            var tempFileDecrypted = Path.GetTempFileName();
+
+            try
+            {
+                var message = "This is a test with umlauts äüö.";
+                await File.WriteAllTextAsync(tempFileInput, message);
+
+                var password = "test password";
+                var previousIterations = 1_000;
+                var upgradedIterations = 1_000_000;
+
+                await using (var outputStream = File.OpenWrite(tempFileEncryptedPrevious))
+                {
+                    await using var inputStream = File.OpenRead(tempFileInput);
+                    await CryptoProcessor.Encrypt(inputStream, outputStream, password, previousIterations);
+                }
+
+                await using (var outputStream = File.OpenWrite(tempFileReEncrypted))
+                {
+                    await using var inputStream = File.OpenRead(tempFileEncryptedPrevious);
+                    await CryptoProcessor.UpgradeIterations(inputStream, outputStream, password, previousIterations, upgradedIterations);
+                }
+                
+                Assert.That(await File.ReadAllBytesAsync(tempFileEncryptedPrevious), Is.Not.EqualTo(await File.ReadAllBytesAsync(tempFileReEncrypted)));
+
+                await using (var outputStream = File.OpenWrite(tempFileDecrypted))
+                {
+                    await using var inputStream = File.OpenRead(tempFileReEncrypted);
+                    await CryptoProcessor.Decrypt(inputStream, outputStream, password, upgradedIterations);
+                }
+                
+                Assert.That(await File.ReadAllTextAsync(tempFileDecrypted), Is.EqualTo(message));
+            }
+            finally
+            {
+                try
+                {
+                    File.Delete(tempFileInput);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileDecrypted);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileEncryptedPrevious);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileReEncrypted);
+                }
+                catch
+                {
+                }
+            }
+        }
+
         [Test]
         public async Task TestChangedPasswordBehaviour()
         {