public void AddiditionalChars()
    {
        var target = new KueiExtensions.RandomString(additionalChars: new char[] { 'a' });

        var actual         = target.Generate(_length);
        var distinctActual = actual.Distinct().ToArray();

        var expected = new char[] { 'a' };

        expected.Should().BeEquivalentTo(distinctActual);
    }
    public void UpperCaseOnly()
    {
        var target = new KueiExtensions.RandomString(userUpperCase: true);

        for (int i = 0; i < _count; i++)
        {
            var actual      = target.Generate(_length);
            var lowerActual = actual.ToUpper();
            Assert.AreEqual(lowerActual, actual);
        }
    }