public void ForbidChars_String()
        {
            // Arrange
            var filter = new CodePointFilter(UnicodeRanges.BasicLatin);

            // Act
            var retVal = filter.ForbidCharacters("xz");

            // Assert
            Assert.Same(filter, retVal); // returns 'this' instance
            Assert.True(filter.IsCharacterAllowed('w'));
            Assert.False(filter.IsCharacterAllowed('x'));
            Assert.True(filter.IsCharacterAllowed('y'));
            Assert.False(filter.IsCharacterAllowed('z'));
        }
        public void ForbidChars_String()
        {
            // Arrange
            var filter = new CodePointFilter(UnicodeRanges.BasicLatin);
            filter.ForbidCharacters('x', 'z');

            // Assert
            Assert.True(filter.IsCharacterAllowed('w'));
            Assert.False(filter.IsCharacterAllowed('x'));
            Assert.True(filter.IsCharacterAllowed('y'));
            Assert.False(filter.IsCharacterAllowed('z'));
        }