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Thursday, May 26, 2011

Defensive programming

Had an interesting conversation with a programmer today. He created a program for updating pricing on books. It allowed you to update the price of one book at a time or to load a list of volume ids (sort of like ISBNs) and batch update the prices.

Many of our partners use Excel to manage their list of books. So the programmer was told the batch screen had to load Excel files.

My first thought when testing the application was, "How can users mess up an Excel file?"

The application required a header row with specific text. What if:
  • there were extra columns
  • a column was missing
  • there was whitespace before or after the text
  • there was no header row
  • the text was all lowercase
  • the text was all uppercase
  • the text was camel cased (ThisIsCamelCase)
Tried all these and each one crashed the program. The programmer was using a third party library to access the Excel spreadsheet. I had used similar libraries in the past and knew these to be problems with those libraries. Essentially, you need to guard against bad data as these libraries don't.

When LAMP (Linux/Apache/MySQL/Php|Perl|Python) programmers access the database, they never assume the data coming in is safe. They check all the data before using it to access the database. This is because hackers will do things like input the following for First Name: "Hacker; DROP TABLE ..." or some other destructive text.

The lesson learned from this is to be a defensive programmer. LAMP programmers know this. I believe this to be true for people using third party libraries but also when using the code from someone else on your own team. If you assume the library does not handle edge cases and ensure the data has been checked before getting passed to the other programmer's code.

If you assume all code (third party libraries, your old code, code from other programmers on your team, etc.) does not handle code properly and check the inputs before passing them along to that code, your applications will be much more solid.

To the testers reading this, assume all programmers will assume someone else will take care of guarding against bad inputs. So think of all the bad inputs you can and send them in. You'll usually find they make it quite far before someone handles them. Often it will be the operating system that handles this with a crypt error dialog and a crash.

Sunday, May 22, 2011

Asking for automation help

I've noticed a trend on help forums and groups. When people ask for help with their automation that often post what they tried and that it did not work.

They don't give any information about their environment, versions of the various software involved or the code they are trying to automate.

Asking for help with your automation is similar to filing a defect report.

  • Specify a summary of the problem
  • Give a description of the environment (OS, browser, etc.)
  • Tell them what you did, what you expected to happen and what actually happened.
There is one additional piece of information you normally put in a defect report. You normally specify which build the defect appeared in. This is because the developer fixing the bug can find the appropriate code given a build number.

When asking people outside your organization for help with an automation problem, we don't have access to your source code. So a build number does not help us. What we need instead is a code snippet. If you are testing a web site, give us the relavent HTML code you are trying to automate.

Without these bits of information it would be impossible to solve the problem. At best, you will get a lot of guessing. If you are lucky, someone will make a lucky guess or say something which makes you realize what the problem really is. However, if you want a quicker response to your questions give us the information we need to reproduce the problem and solve it.