Imports Xunit Public Class IsbnVerifierTests Public Sub Valid_isbn() Assert.True(IsValid("3-598-21508-8")) End Sub Public Sub Invalid_isbn_check_digit() Assert.False(IsValid("3-598-21508-9")) End Sub Public Sub Valid_isbn_with_a_check_digit_of_10() Assert.True(IsValid("3-598-21507-X")) End Sub Public Sub Check_digit_is_a_character_other_than_x() Assert.False(IsValid("3-598-21507-A")) End Sub Public Sub Invalid_check_digit_in_isbn_is_not_treated_as_zero() Assert.False(IsValid("4-598-21507-B")) End Sub Public Sub Invalid_character_in_isbn_is_not_treated_as_zero() Assert.False(IsValid("3-598-P1581-X")) End Sub Public Sub X_is_only_valid_as_a_check_digit() Assert.False(IsValid("3-598-2X507-9")) End Sub Public Sub Valid_isbn_without_separating_dashes() Assert.True(IsValid("3598215088")) End Sub Public Sub Isbn_without_separating_dashes_and_x_as_check_digit() Assert.True(IsValid("359821507X")) End Sub Public Sub Isbn_without_check_digit_and_dashes() Assert.False(IsValid("359821507")) End Sub Public Sub Too_long_isbn_and_no_dashes() Assert.False(IsValid("3598215078X")) End Sub Public Sub Too_short_isbn() Assert.False(IsValid("00")) End Sub Public Sub Isbn_without_check_digit() Assert.False(IsValid("3-598-21507")) End Sub Public Sub Check_digit_of_x_should_not_be_used_for_0() Assert.False(IsValid("3-598-21515-X")) End Sub Public Sub Empty_isbn() Assert.False(IsValid("")) End Sub Public Sub Input_is_9_characters() Assert.False(IsValid("134456729")) End Sub Public Sub Invalid_characters_are_not_ignored_after_checking_length() Assert.False(IsValid("3132P34035")) End Sub Public Sub Invalid_characters_are_not_ignored_before_checking_length() Assert.False(IsValid("3598P215088")) End Sub Public Sub Input_is_too_long_but_contains_a_valid_isbn() Assert.False(IsValid("98245726788")) End Sub End Class