XUnit与MSTest解密结果不一致，原因何在？

我在对以下DecryptString解密方法进行单元测试时，发现使用MSTest和XUnit执行测试得到的结果不同，希望找到问题原因：

public static string DecryptString(string cipherText)
{
    byte[] initVectorBytes = Encoding.UTF8.GetBytes(InitVector);
    byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
    PasswordDeriveBytes password = new PasswordDeriveBytes(StrEncriptyPass, null);
    byte[] keyBytes = password.GetBytes(Keysize / 8);
    RijndaelManaged symmetricKey = new RijndaelManaged();
    symmetricKey.Mode = CipherMode.CBC;
    ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);
    MemoryStream memoryStream = new MemoryStream(cipherTextBytes);
    CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
    byte[] plainTextBytes = new byte[cipherTextBytes.Length];
    int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
    memoryStream.Close();
    cryptoStream.Close();

    string result = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

    return result;
}

测试情况对比 #

• MSTest测试结果正常：解密后能正确得到值"Testando encriptação"，测试代码如下：

[TestMethod()]
public void DecryptStringTest_DecryptString_ReturnsEqual()
{
    var decryptedActual = DecryptString("r2AegGm+zAYmaRL4i+62O2IJrhcHyPsWxHoDZ7bMimI=");
    var esperado = "Testando encriptação";

    Assert.AreEqual(decryptedActual, esperado);
}

• XUnit测试结果异常：解密后仅得到"Testando encript"，缺失了"ação"部分，测试代码如下：

[Fact]
public void DecryptStringTest_DecryptString_ReturnsEqual()
{
    var decryptedActual = DecryptString("r2AegGm+zAYmaRL4i+62O2IJrhcHyPsWxHoDZ7bMimI=");
    var esperado = "Testando encriptação";

    Assert.Equal(decryptedActual, esperado);
}

调试发现的细节 #

调试时注意到，byte[] plainTextBytes = new byte[cipherTextBytes.Length];这一行在两个测试框架中的执行表现不同：

• cipherTextBytes.Length在两个框架中均为32；
• XUnit中plainTextBytes仅填充到索引15；
• MSTest中plainTextBytes填充到索引21。

看起来XUnit似乎影响了该方法的执行逻辑。已知参数信息：Keysize=256，InitVector为16字符的字符串，StrEncriptyPass为同长度文本。

内容的提问来源于stack exchange，提问作者SanderM