Testing and Debugging

Example

Write a program to get an employee ID and a password from a user.

First, the program should repeatedly prompt the user for an ID until the user enters a valid ID.
Then the program should repeatedly prompt the user for a password until the user enters a valid password.

An ID is valid if it is a 7 digit number (and the first digit can't be 0).

A password is valid if it meets the following two criteria:

it is at least 6 but no more than 10 character long
the first character is a letter or an underscore

First draft of code:

done = 0;
id = input('Enter your employee ID: ');
while ~done
    if id < 1000000 || id > 9999999
        id = input('Invalid ID. Enter your ID: ');
    else
        done = 1;
    end
end

done = 0;
while ~done
    passwd = input('Enter your password: ', 's');
    if length(passwd) < 6 || length(passwd) > 10
        disp('invalid – bad length')
    elseif ~( isletter(passwd(1)) || passwd(1) == '_' )
        disp('invalid – must start with letter or _')
    else
        done = 1;
    end
end

Testing

What user input should be used to have adequate test coverage?

positive test cases
negative test cases
boundary test cases

Types of errors

Syntax errors

Semantic errors

Side note: warnings vs errors in MATLAB

Debugging

Using a debugger

set breakpoint
step through code
- step over function
- step into function
- step out of function
- continue to next breakpoint
see variable values