defensive design and testing

Defensive design is an approach to software development where every possible input from a user is considered to anticipate all of the ways a user could misuse a program.

Robust is ensuring that the final program is reliable for all users.

False. Some errors can occur in software that cannot be foreseen by the developer when writing the software.

Peripheral errors are caused when peripherals don't perform as intended. For example, printers running out of paper, ink or having a paper jam.

Disk errors are errors that can occur on disk drives like running out of disk space, files/folders not being found, or corrupted files.

Communication errors are errors that can occur when a program's connection to a host server is lost.

Authentication is the process of ensuring that a system is secure by asking the user to complete tasks to prove they are an authorised user of the system.

A CAPTCHA is a method of authentication where a user must complete a task to prove they are not a bot submitting data.

True. Allowing users to recover passwords via email/SMS is a method programmers can use to authenticate users.

False. Authentication is done because bots can submit data in online forms.

Input validation is code which is used to check that an input from a user is acceptable and that it matches the requirements of the program.

A length check is a type of input validation that checks the length of a string input. E.g. ensuring a password is more than 8 characters

A type check is a type of input validation that checks the data type of a field input. E.g. ensuring a user's age has been entered as an integer

A range check is a type of input validation that ensures a numeric input falls within a particular range. E.g. a user's age falls between the digits 0-110

A presence check is a type of input validation that checks if any data has been entered in a field. E.g. a user's name field has not been left blank

A format check is a type of input validation that ensures the data has been entered in the correct format. E.g. a date has been entered as DD/MM/YYYY

False. There can be occasions where more than one type of validation will be used on a field.

The 5 main categories of input validation are:

password_length = len(password)

The isdigit() method checks if a string contains only digits. It returns True if all characters are digits, False otherwise.

Program maintainability is used to ensure programmers can easily understand what a program is doing months or years after having first written it.

Commenting of code is used for program maintainability to explain the purpose of the code in a particular section.

White space is used for program maintainability to make each section clear and easy to see.

Indentation is used for program maintainability to show each instance of selection and iteration and make it clear which code belongs to which clause.

Sensible variable names are used for program maintainability so the name explains what the variable or data structure does to prevent confusion.

Using sub-programs like functions or procedures is for program maintainability to split code into reusable sections and increase overall structure.

False. Program maintainability is important to ensure the programmer can understand the code months or years later.

Using maintainability features makes the code easier to:

Debugging is the process of finding and resolving errors or defects within a program.

The features that promote maintainability are:

The purpose of testing programs is:

Iterative testing is a type of testing where each part of the program is tested during the development of the program.

Final testing is a type of testing done at the end of development.

True. Iterative testing means repeatedly testing the program while continuing to make changes and improvements during development.

The two main types of testing are iterative testing and final testing.

Normal data is data that falls within the expected range for testing a program against real data during final testing.

Boundary data is data at the minimum or maximum values of the expected range for testing during final testing.

Erroneous data is invalid or incorrect data used for testing to check how the program handles errors during final testing.

False. Alpha and beta testing are types of final testing.

Erroneous

A syntax error is an error that breaks the grammatical rules of a programming language and stops it from running.

A logic error is incorrect code that allows the program to run, but produces an incorrect or undesired output.

True. Syntax errors are easily identifiable as the IDE will provide information about what the error is to help fix it.

Look at the line of code above the one given in the error message, as that may contain the actual syntax error.

name = input("Enter your name")print("Nice to meet you", name) Line 1: missing bracketLine 2: uppercase P on print functionLine 2: missing "

True. Areas to check for logic errors are logical operators (<, >, ==, !=), Boolean operators (AND, OR, NOT) and division by 0.

age = input(int(input("Enter your age: "))if age > 11 or age < 18: print("You are now in secondary school!")else: print("You are not in secondary school!") Entering 21 outputs "You are now in secondary school!" exposing that the incorrect Boolean operator OR was used instead of AND.

False. Logic errors are harder to find than syntax errors as the program still runs, making it more difficult to find them

A normal test is when the user enters data that should be accepted in the program.

A boundary test is when the user enters data that is on the edge of what is acceptable.

An erroneous test is when the user enters data of the wrong data type.

An invalid test is when the user enters data of the right data type but outside of what is accepted.

The 4 main categories of tests are:

Example normal test:

Example boundary test:

Example erroneous test:

Example invalid test:

True. Invalid tests are carried out to test the robustness of the program.