In order to assist in debugging failing test (especially when running them on remote machines without access to a debugger), it can often be helpful to add diagnostic output that is separate from passing or failing test results. xUnit.net offers two such methods for adding output, depending on what kind of code you're trying to diagnose.
If you used xUnit.net 1.x, you may have previously been writing output to
Trace. When xUnit.net
v2 shipped with parallelization turned on by default, this output capture
mechanism was no longer appropriate; it is impossible to know which of the
many tests that could be running in parallel were responsible for writing
to those shared resources. Users who are porting code from v1.x to v2.x
should use one of the two new methods instead.
Unit tests have access to a special interface which replaces previous usage of
Console and similar mechanisms:
In order to take advantage of this, just add a constructor argument for this
interface, and stash it so you can use it in the unit test.
As you can see in the example above, the
WriteLine function on
ITestOutputHelper supports formatting arguments, just as you
were used to with
In addition to being able to write to the output system during the unit
test, you can also write to it during the constructor (and during your
IDisposable.Dispose, if you choose to have
one). This test output will be wrapped up into the XML output, and most
test runners will surface the output for you as well.
To see output from
dotnet test, pass the command line option
Output for unit tests are grouped and displayed with the specific unit test. Output from extensibility classes, on the other hand, is considered diagnostic information. Most runners require you to enable diagnostic output either explicitly with a command line option, or implicitly on an assembly-by-assembly basis by using configuration files.
Each extensibility class has its own individual constructor requirements.
In addition, they can take as their last constructor parameter an
IMessageSink that is designated solely for sending
diagnostic messages. Diagnostic messages implement
xunit.abstractions. If you're linked against
xunit.execution, there is a
class in the
Xunit.Sdk namespace available for your use.
The extensibility interfaces which currently support this functionality are:
Here is an example of using it in a test case orderer:
Then after enabling diagnostic messages in your configuration file, when run, Visual Studio's output window contains a Tests tab which contains the information from running the tests, including the diagnostic message:
To see this output, open the Output window in Visual Studio (from the main menu: View > Output), and in the "Show output from" drop down, select "Tests".