10 steps to testing the bullet proofing user inputs
or how to avoid being caught by nasties when your script goes live!
1. Test it works with intended entries.
It's not going to be much good if it falls over when someone entered a valid piece of data!
2. Test it works (fails correctly) with erroneous entries.
Does it reject entries that should be rejected? Does it place the invalid text back in the form for the user to correct it? Does it also "sticky" the other fields, including selects, checkboxes and radio buttons, so that the user doesn't have to re-enter them? Does it offer a good explanation to the user of what the error was, and what inputs are acceptable?
3. Test it acts appropriately with inputs that include awkward characters and sequences
such as < and " and ' and & and ../ and .htaccess ... and 3.5
where you've asked for a whole number. These are all important "security issues"; you should check that you're protected against ugly display echos if someone enters an HTML tag, SQL injection attacks, and file names that are reserved or navigate the directory tree.
4. Test it against a whole file of inputs
There may be some "odd" cases you haven't thought of in the testing above. Do you have a whole file of data / inputs that you can run the script against? Example of what you might find
- a user name gets confused with another user name that's a shortened form of it. I recall having "issues" with a computer called seal
and another called sealion
5. Test it works without cookies and on different browsers.
6. How do you implement your acceptable user policy?
If your script is publishing the information entered on your site, how do you monitor for acceptable content? If it's a voting script, have you prevented one person rigging the system by multi-voting? If it's an online test, have you prevented your user selecting the back button and correcting his answers when you've told him he got a question wrong?
7. Have your colleague test that it works for him / her.
Even with all of the above, you may overlook something. Or what is obvious
to you might not be to someone else (e.g. is the submit button clear ...). Better to find this sort of thing out before you've got 000s of users.
8. Have the person who commissioned the script test that it works for him / her.
Very much worthwhile having your paymaster on site, and after following the steps above the script should be impressibe in its robustness. Oh - and if it goes pear-shaped later, you did
have the approval of the commissioner.
9. Release to some "tame" customers.
Chances are that everyone who's used the script up to this point has been deeply involved and knows what it's about. Having a few customers look and provide feedback at a late stage will alert you to anything which is blindingly obvious in-house but not at all clear to Joe Public.
10. Release to the world.
... with a feedback link, and do make sure that you have a look at the log files and see the pattern of use. (written 2005-08-27, updated 2008-05-17)
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