How can you possibly test modern software fully?

Pairing up for fun and profit

Providing a secure and efficient Helpdesk

The common assumption about software testing is that "more is better", and testing all the possible states and variable combinations guarantees you will find all the bugs.

In the real world, however, there is not enough time or enough testers to test every combination of every variable. Not all bugs will be found, making quality assurance a risk management discipline. How can you validate that your product is ready to ship within reasonable time and cost parameters? In other words, how can you manage the risk of not testing everything? One solution is to use structured testing methodologies, supported by proper tools, which help you quantifiably manage this risk.

Practically speaking, the role of quality assurance is to reduce the risk of these bugs ending up in the final product. Software complexity puts a huge burden on QA teams, which are typically much smaller than the development teams writing the software (it's even worse if there isn't a QA team and developers take on the role part time). It is also very easy for one developer to write a small amount of code that requires a significant amount of testing to ensure it functions properly in all situations.

For example, you have to test a dialog box with three drop-down lists to see if any of the combinations cause the program component to fail. The first list has five options, the second has eight options, and the third has three; see Figure 1:

Figure 1.

To determine all the possible combinations, you can create a matrix like the following (Figure 2):

Figure 2.

As you continue adding combinations, you discover that 120 test cases are required to cover all the possible combinations. You can also determine the number of combinations by multiplying the number of values available in each option (5 x 8 x 3 = 120). If each test takes around two minutes to perform, you are faced with about 4 hours of testing on a simple dialog box. What if you need to test 100 dialog boxes? What if some dialog boxes contain 15 options instead of three?

Now take the concept of complete coverage a step further and consider environmental variables such as operating system, database, and hardware components. How do you ensure you find a bug that occurs only when the application is running on Windows XP and is using MySQL without testing all the possible OS and database combinations?

These examples demonstrate how quickly complete coverage becomes unmanageable. Luckily, you can find most bugs without testing all the combinations. The simplest bugs are single-mode faults, which occur when one option causes a problem regardless of the other settings. For example, a printout is always smeared when you choose the duplex option in the print dialog box regardless of the printer or the other selected options.

Another type of bug is one that occurs when two options are combined - the printout is only smeared when duplex is selected and the printer is a model 394. These are called double-mode faults. Finally, multi-mode faults, which occur when three or more settings produce the bug, are the types of problems that make complete test coverage seem necessary.

However, complete coverage is usually not necessary. A study by Telcordia Technologies found that "most field faults were caused by either incorrect single values or by an interaction of pairs of values" (Cohen, et al. 1996). Another study of the software in medical devices showed that only three of the 109 failures resulted from the combination of more than two conditions (Wallace, 2000).

If you have limited time and resources, you want to find the most common bugs and those that present the highest risk. Suppose the printer error only occurs when the operating system is Windows, the print option is set to duplex, the print quality is draft, and the collate option is not selected. Is it worth your time to find that bug? Does the bug present a big enough risk to the user or application that it will even require a software fix?

Except in the rare cases where life and death are at stake, you can achieve a statistically acceptable level of quality by testing less than 100 per cent of the combinations. One approach to doing this is called pair-wise or all-pairs testing.

Internet Security Threat Report 2014

More from The Register

next story
Microsoft on the Threshold of a new name for Windows next week
Rebranded OS reportedly set to be flung open by Redmond
'In... 15 feet... you will be HIT BY A TRAIN' Google patents the SPLAT-NAV
Alert system tips oblivious phone junkies to oncoming traffic
Apple: SO sorry for the iOS 8.0.1 UPDATE BUNGLE HORROR
Apple kills 'upgrade'. Hey, Microsoft. You sure you want to be like these guys?
SMASH the Bash bug! Apple and Red Hat scramble for patch batches
'Applying multiple security updates is extremely difficult'
ARM gives Internet of Things a piece of its mind – the Cortex-M7
32-bit core packs some DSP for VIP IoT CPU LOL
Lotus Notes inventor Ozzie invents app to talk to people on your phone
Imagine that. Startup floats with voice collab app for Win iPhone
'Google is NOT the gatekeeper to the web, as some claim'
Plus: 'Pretty sure iOS 8.0.2 will just turn the iPhone into a fax machine'
prev story


Providing a secure and efficient Helpdesk
A single remote control platform for user support is be key to providing an efficient helpdesk. Retain full control over the way in which screen and keystroke data is transmitted.
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.
Beginner's guide to SSL certificates
De-mystify the technology involved and give you the information you need to make the best decision when considering your online security options.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.
Secure remote control for conventional and virtual desktops
Balancing user privacy and privileged access, in accordance with compliance frameworks and legislation. Evaluating any potential remote control choice.