Guest Unit Tests
For some time now, unit testing has proven to be a valuable quality-assurance method. The technique allows a computer to grind through all of the possible code that a change might destabilize with subtle side-effects. This approach not only preserves much higher code-quality but also spares developers from many tedious hours (and migraines) spend on debugging.
Wine has had its own suite of Conformance Tests since ca. 2003 to keep bugs from sneaking into the source tree. Since the tests can also be run on Windows, this has been a great black-box method to collect data on how wine's behavior still differs from Windows'. This is especially true of bugs-become-features and other undocumented parts of the API that real-world programs rely on.
That said, we can only develop so many tests ourselves, but fortunately there are even more ways to let the machines do some debugging for us. Since the goal is for wine to interact with Windows API programs indistinguishably from Windows, we can use high-quality, mature test suites from other projects to spot deviations. You can think of this as very similar to how chemists use standard reagents for precise results, even if they don't have direct access to the tools that set the standard.
If you have a test-suite already designed to run on Windows, then you should be able to just execute it in Wine and watch the sparks fly. Just be sure to also run the test suite on at least one or two Windows machines for comparison, especially if it's not a particularly mature test-suite. Errors that appear on both may still be valid problems in wine, but the deviations should have priority.
One particularly nice class of test-suites to try are ones developed for programming languages. Many are totally open-source, made to be cross-platform, and easy to run. For example, if you've installed a recent Windows release of Python3 to your wine prefix, you can try running the default test suite with one line:
wine 'c:\path\to\python.exe' -m test
The one trade-off with language test-suites is that the interpreter / compiler involved inevitably adds another layer between the actual test and wine. This can make it a little harder to interpret failed test results sometimes.
By contrast, project unit-tests written in C or C++ may not always be packaged as nicely, but they should run well on wine. Furthermore, by eliminating any intervening software and staying closer to bare metal, these tests will often point directly to the issue in wine, making them a great tool for digging up bugs.
Say you've found something with a foreign test-suite and want to report a bug on our Bugzilla. To make tracking bugs easier, consider appending the project's short name in parentheses at the end of your report title. For example, "(Apache)", "(Firefox)", or "(Ruby)"
Projects with Buildbots
"Success story" pages by build-and-test systems, aka "continuous integration" (CI), are one great way to find test-suites. One can typically follow links to the project's actual test-rig instance, with details about the project's current status vis-a-vis different configurations, including Windows. Every project that's been doing fine on Windows for a while is a prime candidate for testing against wine.
Many of the projects may not necessarily be built on Windows, but here are grocery-list pages for some different CI suites:
Of course, if you've stumbled across another project with a test-suite that performs solidly on Windows, you're always free to use it.
A major reason we prefer test-suites from projects using CI is that there's a higher risk of flaky tests otherwise. It's often only after a project starts running their tests continuously that the flawed and chaotic unit tests are exposed and fixed. Don't be discouraged from trying an interesting test-suite, even if the project doesn't test continuously. Just keep in mind that such test results will be viewed as less reliable by default.
There are a few other interesting tools out there that may not count as full test-suites, but could still serve a useful function for testing wine's compatibility with Windows.
The first is a small app called Control Spy, designed and provided by Microsoft itself for debugging Windows control objects. In the past, this tool helped us uncover a few bugs.
At one point, there was a debate on Bugzilla about whether using Control Spy v2 to test wine violates Microsoft's EULA. If you are interested in using Control Spy to debug wine, you should definitely ask the wine-devel mailing list first and wait for an ok.
Another handy program, which can also open up new horizons for testing on wine, is AutoHotkey. Besides automating many everyday tasks on Windows (and wine), with a little ingenuity, you can whip up your own bespoke automated tests. At one point in fact, Austin English was developing a script framework called Appinstall; it would use AutoHotkey to automatically test installation and more for a wide range of programs. This project has been dormant for a while, but may be revived in the future (see Winezeug for more info).
Finally, while there haven't been any updates for newer versions of Windows, FrancoisGouget had the inspired and sneaky idea to re-purpose the code snippets from programming books into a simple test-suite of sorts. You can read more about his method and observations on his web-page.