The Software Migration Testing Challenge Agile Testing

The software migration challenge was slightly unusual in the sense that we were not changing the behavior of the existing system in any way.The only thing that was really important from a functional testing perspective, therefore, was for the system to behave in exactly the same way before and after the completion of the software migration.

Since there were no existing tests and the internal design of the system was not well understood,we judged that the most effective way to regression test the software migration would be to use an automated record/playback (or capture–replay) style of testing tool at the system interface level. The system had a small user interface that could be tested manually, but the rest of the system was operated via XML (Extensible Markup Language) message interfaces to other systems. It was therefore relatively straightforward to create a message recorder that extracted system messages from the input and output message logs.Starting with a fresh system database, a test harness then took the messages, replaying the input messages and verifying the outputs.

The system users were engaged to help develop and run through a set of test cases, which were duly recorded. The resulting scripts were then run before migration and against each incremental release of the migrated system.

Within the scope of the migration activity, this mechanism worked very well. The system needed to be built and deployed to the application server before any testing could commence, but this was appropriate given the lack of any functional change.

One minor problem encountered was that sometimes parts of the output messages could be difficult to predict – for example, if they were time-dependent. Our solution to this problem was to arrange for the system time to be artificially fixed by the test. It would also have been possible, although involving slightly more work, to write a more intelligent message verifier.



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