Testing Tradeoffs and Project Risk: A Case Study


Between extreme opinions of what is testing “overkill” and what is “essential,” there sometimes exists a reasonable middle path. In this field report, Payson identifies an example of risk mitigation and the evolution of the analysis that brought him there.


The project had issues. It was a two-year project intended to swap an aging legacy application for a commercial product. The vendor’s off-the-shelf software required some customization and extension for the (very, very large) customer.

Among other things, the application scheduled classes and tracked attendance.  It also docked the pay of people who failed to attend classes for which they were scheduled.

There were a number of extenuating circumstances that led the project to its troubled state, but they are not relevant to this story. Suffice it to say that a new project manager (a friend and client) had been brought in late to the process—about six weeks from the proposed go-live date—and had just discovered that the only planned testing was users banging on keyboards to assure that the commercial application “met their needs.” What the users could touch was mostly the non-modified parts of the commercial application, and finding errors there was unlikely.

When we looked under the covers, we discovered the customizations required of the commercial application involved swapping about a dozen files with existing customer legacy applications. These interfaces were direct replacements of files that the legacy application (being retired) had used to pass data to other client systems. Existing plans omitted any testing of these interfaces. Yikes!

When asked to help triage the situation, my first assumption was: “If the legacy applications that consume the interface files are programmed defensively (e.g., validating all the data they received before further processing), then perhaps exhaustive testing won’t be necessary.” I was thinking that bogus data would be detected and that this might allow us to go live and  then monitor for problems while we retroactively reviewed and tested.

A quick consult with the application team that supported the consuming systems dashed those hopes. The legacy systems had been built to “trust” the files they consumed and used them without validation. (Note to developers: “Trusting” interfaces decreases modularity in the future. It’s faster and cheaper in the short term, but sometimes you repeatedly pay a premium for the shortcut.)

Armed with this information, my next thought was: “Unfortunate. If we don’t want to contaminate the legacy environment, perhaps we should perform complete data validation of the incoming interface files.” This was a reasonable and conservative default assumption to protect the consuming systems. We could have stopped there and insisted that validation programs be created for each of the interface files, but that would likely threaten the planned go-live date. To estimate this effort and to confirm whether it was necessary, I needed to get more information about the interface files—their complexity, size, and how their consuming systems used them.

I rolled up my sleeves and dove into the specifications. It wasn’t as bad as I had feared at first. Of the dozen or so files exchanged, I discovered the following:

  • Several fed internal reports and could probably be “eyeballed” for quality purposes after going live. The consequence of bad data would be minor annoyance and easily detected. The reports were consumed internally. It was probably safe to go live without testing these and then monitor the reports in the interim while testing more extensively after going live.
  • Some of the files passed information about scheduled classes back and forth —the worst case being that a class might be scheduled for February 30 or have zero slots available. Since this information was fed from user-entered data in the new commercial component, it was reasonable to assume that the commercial application did some preliminary validation. Furthermore, the consequences of erroneous data were not fatal in an application context. The

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