diff --git a/Encrypter Tests/EncrypterTests.cs b/Encrypter Tests/EncrypterTests.cs
index bc1d3b8..b6874e2 100644
--- a/Encrypter Tests/EncrypterTests.cs	
+++ b/Encrypter Tests/EncrypterTests.cs	
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Security.Cryptography;
 using System.Text;
 using System.Threading.Tasks;
 using Encrypter;
@@ -21,5 +22,111 @@ namespace Encrypter_Tests
             var decryptedMessage = await CryptoProcessor.DecryptString(encryptedData, password);
             Assert.That(decryptedMessage, Is.EqualTo(message));
         }
+
+        [Test]
+        public async Task TestEmptyMessage()
+        {
+            var message = string.Empty;
+            var password = "test password";
+
+            var encryptedData = await CryptoProcessor.EncryptString(message, password);
+            var decryptedMessage = await CryptoProcessor.DecryptString(encryptedData, password);
+            Assert.That(decryptedMessage, Is.EqualTo(message));
+        }
+
+        [Test]
+        public async Task TestNoMessage()
+        {
+            string message = null;
+            var password = "test password";
+
+            try
+            {
+                var encryptedData = await CryptoProcessor.EncryptString(message, password);
+                Assert.Fail("Should not be reached!");
+            }
+            catch(CryptographicException e)
+            {
+                Assert.That(true);
+            }
+        }
+
+        [Test]
+        public async Task TestTooShortPassword4Encryption()
+        {
+            var message = "This is a test with umlauts äüö.";
+            var password = "test";
+
+            try
+            {
+                var encryptedData = await CryptoProcessor.EncryptString(message, password);
+                Assert.Fail("Should not be reached!");
+            }
+            catch (CryptographicException e)
+            {
+                Assert.That(true);
+            }
+        }
+
+        [Test]
+        public async Task TestTooShortPassword4Decryption()
+        {
+            var message = "This is a test with umlauts äüö.";
+            var password = "test password";
+
+            var encryptedData = await CryptoProcessor.EncryptString(message, password);
+            
+            try
+            {
+                var decryptedMessage = await CryptoProcessor.DecryptString(encryptedData, password[..4]);
+                Assert.Fail("Should not be reached!");
+            }
+            catch (CryptographicException e)
+            {
+                Assert.That(true);
+            }
+        }
+
+        [Test]
+        public async Task TestSimpleEnAndDecryptionWithASCII()
+        {
+            var message = Encoding.ASCII.GetString(Encoding.Convert(Encoding.UTF8, Encoding.ASCII, Encoding.UTF8.GetBytes("This is a test without umlauts.")));
+            var password = "test password";
+
+            var encryptedData = await CryptoProcessor.EncryptString(message, password);
+            var decryptedMessage = await CryptoProcessor.DecryptString(encryptedData, password);
+            Assert.That(decryptedMessage, Is.EqualTo(message));
+        }
+
+        [Test]
+        public async Task TestChangedPassword()
+        {
+            var message = "This is a test with umlauts äüö.";
+            var password1 = "password!";
+            var password2 = "password.";
+
+            var encryptedData = await CryptoProcessor.EncryptString(message, password1);
+
+            try
+            {
+                var decryptedMessage = await CryptoProcessor.DecryptString(encryptedData, password2);
+                Assert.Fail("Should not be reached!");
+            }
+            catch (CryptographicException e)
+            {
+                Assert.That(true);
+            }
+        }
+
+        [Test]
+        public async Task TestSimpleExtensionMethods()
+        {
+            var message = "This is a test with umlauts äüö.";
+            var password = "test password";
+
+            var encryptedData = await message.Encrypt(password);
+            var decryptedMessage = await encryptedData.Decrypt(password);
+            Assert.That(decryptedMessage, Is.EqualTo(message));
+        }
     }
 }