Taking the Drudgery Out of QA with Live Unit Testing in Visual Studio 2017

Howdy readers, Lafe here. About once a month, my partner in crime, Rich Seeley, has been doing technical takeovers of this blog. Here's his latest post, which looks at the Live Unit Testing feature introduced in Visual Studio 2017.

Write the code. Stop. Test the code. Try to figure out where the bug is. Try out a fix. Test again. Maybe it works and maybe it doesn't. Maybe it will get through QA or maybe it won't. This is what Joe Morris, senior program manager, Visual Studio and .NET Team, calls old school testing. None dare call it drudgery.

But for developers working with Visual Studio 2017 Enterprise Edition old school testing methods have been replaced with a cool new feature called Live Unit Testing. It allows you to run testing as you code, so you can immediately see lines of code that aren’t passing as well as lines that aren't being covered by any test. You can fix the failing code on the fly and know immediately if it passes. You can also quickly apply as test to uncovered code and see if it passes.

"It will tremendously improve your coding productivity and quality of code by showing the unit test and code coverage live in the editor while you're coding," Morris explains in a short video demoing Live Unit Testing. Usually words like "tremendously improve" are marketing hype but looking at Live Unit Testing in action it appears to be the real deal.

To contrast Live Unit Testing with old school testing, Morris shows us what he used go through to run tests in the pre-Visual Studio 2017 world.

The test had to be run "manually" and they could then be viewed in the Test Explorer window. The trouble was Test Explorer didn't tell you very much. It was the equivalent of a GPS system that would leave you on the edge of a forty-square mile area wherein the restaurant you were looking for might be located.

"I would look at the failed test," Morris said. "It tells me that the test failed in line 43. But that is not much useful info. To see more data on the failed test I would typically run Code Coverage Results for failed test. It tells me what blocks are covered and not covered. It still doesn't show any visualization in the code editor. I can click on show code coverage in the blocks in the editor. Even then it is not easy to figure out which one is covered and not covered or failing."

By contrast, Live Unit Testing is...well...live and quick and rather than looking for a needle in a haystack it pinpoints where the problems are.

So forget Test Explorer. To enable Live Unit Test you go to the Test menu where you select Live Unit Testing from a drop down menu and click on Start.

Within a few seconds you will see glyphs showing up in the left hand column of your code editor. Green checks on a line indicate tests covered by Unit Testing are passing. Red Xs indicate a line is failing the covered unit test. Blue dashes indicate no Unit Test coverage. So it’s a matter of stopping and making fixes on the red and being good to go on the green. Meanwhile blue dashes remind you to find a test to make sure the blue line is okay.

Or as Microsoft describes it: "This will gently remind you to write unit tests as you are making bug fixes or adding features."

With the lines marked with red glyphs, you are able to zero in using a popup that shows specifically which test it is passing or failing. Once you know what test is failing, you are pretty close to understanding what needs to be fixed. And when you make the fix to the line the test results show up almost instantaneously.

"I identify the bug in my code," Morris explains. "I need to add another line of code to fix the code. As soon as I make that change the state of the code changes from red crosses to green checks indicating my code is passing the unit test now."

Where there is a blue dash showing that line of code is covered by zero tests, the fix is also swift. By going to the Unit Test window, you can add a test. The test runs and a green check indicates it passed.

Very quickly everything goes to green. By keeping Live Unit Test running as you code, you can make sure your code passed and Unit Test coverage is 100 percent.

"That's very cool," Morris says. "I can see that all my lines of code are covered by a test and they all have a green check."

The feature works with C# and VB projects for .NET and supports the MSTest, xUnit and NUnit test frameworks.

"It uses VB and C# compilers to instrument the code at compile time," Microsoft explains in a Visual Studio blog covering the new feature. "Next, it runs unit tests on the instrumented code to generate data which it analyzes to understand which tests are covering which lines of code. It then uses this data to run just those tests that were impacted by the given edit providing immediate feedback on the results in the editor itself. As more edits are made or more tests are added or removed, it continuously updates the data which is used to identify the impacted tests."

Posted by Lafe Low on 09/07/2017

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