Live Testing in Visual Studio 2017

While working on this project, I decided that I would see how useful the new feature of “Live Testing” is for TDD.

Once you’ve created your suite of tests, turning live testing on gives you some interesting information:

As you can see, there are some slight contradictions here in what it’s telling me. The first test is failing, the test for Count has a line (which indicates not covered). However, code lens is telling me there are two covering tests.

My suspicion here is that live testing is being too clever for its own good; for example, looking at the tests themselves, shows that only the first Enqueue statement is covered:

My thoughts are that the engine works out where the test fails, and so, in the case above, it’s telling me that the tests are not running the line of code that tests the Count functionality. What I’m guessing is that this is because the tests are failing before that.

I can prove this by creating a further unit test:

And, indeed, this now shows coverage:

As I start to add the functionality, I can quickly see that the tests are now passing:

Changing the way code is written

The interesting thing here is that is promotes two things:
1. Defined tests – if a test covers more than one thing, it will show as uncovered initially
2. Tests first – obviously, there need to be tests to show test coverage

Caveats

1. Annoyingly, by default, you continually have to opt in for live unit testing. It only starts when you select to “Start” live unit testing, and this must be done each time you launch VS. This is configurable, and can be switched on by default in options:

2. If the build fails, it shows nothing.

3. Live testing is only available in Visual Studio Enterprise.

NUnit

One thing that only occurred to me as notable while I was writing this is that the tests that I’ve written are in NUnit. So the Live Testing clearly works with none MSTests, and probably works with anything that’ll show up in Test Explorer / Code Lens.

References

https://blogs.msdn.microsoft.com/visualstudio/2017/03/09/live-unit-testing-in-visual-studio-2017-enterprise/

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