Why doesn't tracing behavior appear to work when added to Autofixture Fixture.Behaviors in an AutoDataAttribute implementation? -

when add new tracingbehavior autofixture fixture instance using

fixture.behaviors.add(new tracingbehavior()); 

i tracing output in r# unit test sessions window.

however, when inherit autodataattribute , add behavior inside attribute's constructor this

i no tracing output, though tests indicate tracingbehavior has been added fixture.behaviors in both scenarios. below 2 simple tests , attribute implementation reproduce.

public class tracingbehaviortests {     [theory, autodata]     public void tracingoutputdisplayedwhenmanuallyaddedtofixture(fixture fixture)     {         fixture.behaviors.add(new tracingbehavior());         var actual = fixture.behaviors.oftype<tracingbehavior>().any();         assert.equal(true, actual); // passes         fixture.create<string>();   // tracing output displayed     }      [theory, tracingfixtureconventions]     public void tracingoutputdisplayedwhenusingtracingfixtureconventionsattribute(fixture fixture)     {         var actual = fixture.behaviors.oftype<tracingbehavior>().any();         assert.equal(true, actual); // passes         fixture.create<string>();   // no tracing output displayed     } }  public class tracingfixtureconventionsattribute : autodataattribute {     public tracingfixtureconventionsattribute()         : base(new fixture())     {         this.fixture.behaviors.add(new tracingbehavior());     } } 

i had little digging figure out why happening.

the reason you're seeing behaviour when use default constructor of tracingbehavior, console.out destination.

when executing test case, xunit.net test runner assigns another textwriter console.out.

this happens before code block in test method executed, explains why first test in op displays trace: when tracingbehavior instance created, console.out already captured textwriter.

however, in second test (using [tracingfixtureconventions] attribute), console.out has not yet been replaced when attribute's constructor runs. so, when test runs, traces the original console.out, since there's no console present, traces void.

you can verify both test cases do log logging file instead:

public class tracingbehaviortests {     [theory, autodata]     public void tracingoutputdisplayedwhenmanuallyaddedtofixture(fixture fixture)     {         using (var tw = file.appendtext(path.combine(environment.currentdirectory, "log.txt")))         {             tw.autoflush = true;             fixture.behaviors.add(new tracingbehavior(tw));             var actual = fixture.behaviors.oftype<tracingbehavior>().any();             assert.equal(true, actual); // passes             fixture.create<string>();   // tracing output logged file         }     }      [theory, tracingfixtureconventions]     public void tracingoutputdisplayedwhenusingtracingfixtureconventionsattribute(fixture fixture)     {         var actual = fixture.behaviors.oftype<tracingbehavior>().any();         assert.equal(true, actual); // passes         fixture.create<string>();   // tracing output logged file     } }  public class tracingfixtureconventionsattribute : autodataattribute {     public tracingfixtureconventionsattribute()         : base(new fixture())     {         var tw = file.appendtext(path.combine(environment.currentdirectory, "log.txt"));         tw.autoflush = true;         this.fixture.behaviors.add(new tracingbehavior(tw));     } } 

the above 'fix' rather fragile, because (as written here) [tracingfixtureconventions] attribute doesn't dispose of tw, if test adorned [tracingfixtureconventions] attribute runs first, log file in use, , other test not able write it.

for now, i'll leave exercise reader figure out how make file logging more robust, if that's cares about. personally, use autofixture tracing troubleshoot, , turn off again once i'm done troubleshooting.