Italian Fiscal Code validation in C#

ValidateFiscalCode.cs

/// <summary>
///     Validate Italian Fiscal Code (https://en.wikipedia.org/wiki/Italian_fiscal_code_card)
/// </summary>
/// <param name="fiscalCode">code to be checked</param>
/// <returns><c>true</c> if checksum is valid, <c>false</c> otherwise</returns>
/// <remarks>
///     Based on: https://gist.github.com/supix/97dfe1e2c4b804bd3721faf4bec1c573
/// </remarks>
public static bool IsFiscalCodeValid(string fiscalCode)
{
    if (fiscalCode == null) return false;

    const string regex =
        @"^(?:[B-DF-HJ-NP-TV-Z](?:[AEIOU]{2}|[AEIOU]X)|[AEIOU]{2}X|[B-DF-HJ-NP-TV-Z]{2}[A-Z]){2}[\dLMNP-V]{2}(?:[A-EHLMPR-T](?:[04LQ][1-9MNP-V]|[1256LMRS][\dLMNP-V])|[DHPS][37PT][0L]|[ACELMRT][37PT][01LM])(?:[A-MZ][1-9MNP-V][\dLMNP-V]{2}|[A-M][0L](?:[\dLMNP-V][1-9MNP-V]|[1-9MNP-V][0L]))[A-Z]$";
    if (!Regex.IsMatch(fiscalCode, regex)) return false;

    #region static maps

    var oddMap = new Dictionary<char, int>
                     {
                         { '0', 1 },
                         { '1', 0 },
                         { '2', 5 },
                         { '3', 7 },
                         { '4', 9 },
                         { '5', 13 },
                         { '6', 15 },
                         { '7', 17 },
                         { '8', 19 },
                         { '9', 21 },
                         { 'A', 1 },
                         { 'B', 0 },
                         { 'C', 5 },
                         { 'D', 7 },
                         { 'E', 9 },
                         { 'F', 13 },
                         { 'G', 15 },
                         { 'H', 17 },
                         { 'I', 19 },
                         { 'J', 21 },
                         { 'K', 2 },
                         { 'L', 4 },
                         { 'M', 18 },
                         { 'N', 20 },
                         { 'O', 11 },
                         { 'P', 3 },
                         { 'Q', 6 },
                         { 'R', 8 },
                         { 'S', 12 },
                         { 'T', 14 },
                         { 'U', 16 },
                         { 'V', 10 },
                         { 'W', 22 },
                         { 'X', 25 },
                         { 'Y', 24 },
                         { 'Z', 23 }
                     };

    var evenMap = new Dictionary<char, int>
                      {
                          { '0', 0 },
                          { '1', 1 },
                          { '2', 2 },
                          { '3', 3 },
                          { '4', 4 },
                          { '5', 5 },
                          { '6', 6 },
                          { '7', 7 },
                          { '8', 8 },
                          { '9', 9 },
                          { 'A', 0 },
                          { 'B', 1 },
                          { 'C', 2 },
                          { 'D', 3 },
                          { 'E', 4 },
                          { 'F', 5 },
                          { 'G', 6 },
                          { 'H', 7 },
                          { 'I', 8 },
                          { 'J', 9 },
                          { 'K', 10 },
                          { 'L', 11 },
                          { 'M', 12 },
                          { 'N', 13 },
                          { 'O', 14 },
                          { 'P', 15 },
                          { 'Q', 16 },
                          { 'R', 17 },
                          { 'S', 18 },
                          { 'T', 19 },
                          { 'U', 20 },
                          { 'V', 21 },
                          { 'W', 22 },
                          { 'X', 23 },
                          { 'Y', 24 },
                          { 'Z', 25 }
                      };

    #endregion static maps

    var total = 0;
    for (var i = 0; i < 15; i += 2) total += oddMap[fiscalCode[i]];
    for (var i = 1; i < 15; i += 2) total += evenMap[fiscalCode[i]];

    return fiscalCode[15] == (char)('A' + total % 26);
}


/* Xunit tests for validator */
[Fact]
public void WhenCodeContainsInvalidControlCharacter_ReturnsFalse()
{
    // example of valid code from https://en.wikipedia.org/wiki/Italian_fiscal_code_card
    var code = "MRTMTT25D09F205X"; // last "X" is invalid, control character should be "Z" 

    // Act
    var valid = ItalianFiscalCodeValidator.IsFiscalCodeValid(code);

    // Assert
    Assert.Equal(false, valid);
}

[Fact]
public void WhenCodeIsTooShort_ReturnsFalse()
{
    // code should contain 15 characters
    var code0 = "";
    var code1 = "M";
    var code2 = "MR";
    var code14 = "MRTMTT25D09F205"; // last "X" is invalid, control character should be "Z" 

    // Act
    var valid0 = ItalianFiscalCodeValidator.IsFiscalCodeValid(code0);
    var valid1 = ItalianFiscalCodeValidator.IsFiscalCodeValid(code1);
    var valid2 = ItalianFiscalCodeValidator.IsFiscalCodeValid(code2);
    var valid14 = ItalianFiscalCodeValidator.IsFiscalCodeValid(code14);

    // Assert
    Assert.Equal(false, valid0);
    Assert.Equal(false, valid1);
    Assert.Equal(false, valid2);
    Assert.Equal(false, valid14);
}

[Fact]
public void WhenNullCodeIsPassed_ReturnsFalse()
{
    // Act
    var valid = ItalianFiscalCodeValidator.IsFiscalCodeValid(null);

    // Assert
    Assert.Equal(false, valid);
}

[Fact]
public void WhenValidCodeIsGiven_ForForeignCitizen_ReturnsTrue()
{
    // example of valid code from https://en.wikipedia.org/wiki/Italian_fiscal_code_card
    var code = "MLLSNT82P65Z404U";

    // Act
    var valid = ItalianFiscalCodeValidator.IsFiscalCodeValid(code);

    // Assert
    Assert.Equal(true, valid);
}

[Fact]
public void WhenValidCodeIsGiven_ReturnsTrue()
{
    // example of valid code from https://en.wikipedia.org/wiki/Italian_fiscal_code_card
    var code = "MRTMTT25D09F205Z";

    // Act
    var valid = ItalianFiscalCodeValidator.IsFiscalCodeValid(code);

    // Assert
    Assert.Equal(true, valid);
}