Dotnet test on multi target project logging on multiple targets

RFCs/0029-Dotnet-Test-MultiTarget-Project-Trx-Logger.md

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+# 0029 Dotnet test on multi target project logging on multiple targets
+
+## Summary
+Dotnet test on a multi-target projects logs only the last target. In multi target project, the log file name provided is being overwritten and ending up in data loss. Issue: [https://github.com/microsoft/vstest/issues/1603](https://github.com/microsoft/vstest/issues/1603)
+
+Example: `dotnet test "--logger:trx;LogFileName=results.trx"` on a multi-target project (e.g. `<TargetFrameworks>netcoreapp2.0;net45</TargetFrameworks>` in the .csproj) causes the logger to only log on the last target.
+
+## Design
+
+### Option 1: Separate folders for separate targets
+
+There are 2 ways to specify the LogFileName.  
+&nbsp;&nbsp;&nbsp;&nbsp;a. Relative filename: `dotnet test "--logger:trx;LogFileName=results.trx"`  
+&nbsp;&nbsp;&nbsp;&nbsp;b. Absolute path: `dotnet test "--logger:trx;LogFileName=d:/results.trx"`  
+
+In case of (a), the trx is generated in the test results directory of the multi target project.
+
+Solution: Generate different target trx files in separate folders inside the test results directory.  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/net45/results.trx  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/netcoreapp2.0/results.trx  
+
+For case (b), the trx file will still be overwritten with a warning.
+
+### Option 2: Specify LogFilePrefix Parameter with timestamp appended
+
+Introduce a LogFilePrefix parameter in trx logger. Example : `dotnet test "--logger:trx;LogFilePrefix=results"`  
+With this, if we want all trx files in a multi target project, instead of specifying a logFileName, we provide a LogFilePrefix.  
+The trx file name prefix is appended with time stamp to generate multi target trx files.  
+
+For example : `dotnet test "--logger:trx;LogFilePrefix=results"` will generate  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_2018-12-24_14-01-07-176.trx  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_2018-12-24_14-01-08-111.trx  
+
+The behavior of  `dotnet test "--logger:trx;LogFileName=results.trx"` will remain same with overwriting being done, and warning to switch to LogFilePrefix.
+
+### Option 3: Specify LogFilePrefix Parameter with target framework appended
+
+Introduce a LogFilePrefix parameter in trx logger. Example : `dotnet test "--logger:trx;LogFilePrefix=results"`  
+With this, if we want all trx files in a multi target project, instead of specifying a logFileName, we provide a LogFilePrefix.  
+The trx file name prefix is appended with target framework to generate multi target trx files.  
+
+For example : `dotnet test "--logger:trx;LogFilePrefix=results"` will generate  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_net451.trx  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_netcoreapp20.trx  
+
+The behavior of  `dotnet test "--logger:trx;LogFileName=results.trx"` will remain same with overwriting being done, and warning to switch to LogFilePrefix.  
+
+When ResultsDirectory is specified, and the solution contains multiple projects with same target,  
+For example,  `dotnet test "--logger:trx;LogFilePrefix=results"`  
+ResultsDirectory: C:\temp, and the solution contains   
+&nbsp;&nbsp;&nbsp;&nbsp; P1 (target net451)   
+&nbsp;&nbsp;&nbsp;&nbsp; P2 (target net451)   
+
+This case will overrride different project results as trx filename will be `C:\temp\results_net451.trx` in both cases.  
+
+### Option 4: Specify LogFilePrefix Parameter with target framework and timestamp appended
+
+Introduce a LogFilePrefix parameter in trx logger. Example : `dotnet test "--logger:trx;LogFilePrefix=results"`  
+With this, if we want all trx files in a multi target project, instead of specifying a logFileName, we provide a LogFilePrefix.  
+The trx file name prefix is appended with target framework to generate multi target trx files.  
+
+For example : `dotnet test "--logger:trx;LogFilePrefix=results"` will generate  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_net451_2018_12-24_14-01-07-176.trx  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_netcoreapp20_2018-12-24_14-01-08-111.trx  
+
+When ResultsDirectory is specified, and the solution contains multiple projects with same target,  
+For example,  `dotnet test "--logger:trx;LogFilePrefix=results"`  
+ResultsDirectory: C:\temp, and the solution contains
+&nbsp;&nbsp;&nbsp;&nbsp; P1 (target net451)  
+&nbsp;&nbsp;&nbsp;&nbsp; P2 (target net451)  
+
+This case will not override results as along with framework, we will append the timestamp.  
+&nbsp;&nbsp;&nbsp;&nbsp; C:\temp\results_net451_2018_12-24_14-01-07-176.trx  
+&nbsp;&nbsp;&nbsp;&nbsp; C:\temp\results_net451_2018-12-24_14-01-08-111.trx  
+
+## Approach Taken
+
+Option 4 : This generates unique test results for different frameworks and different projects. 
+Introduced a LogFilePrefix parameter in trx logger. 
+Example : `dotnet test "--logger:trx;LogFilePrefix=results"`. 
+
+For example : `dotnet test "--logger:trx;LogFilePrefix=results"` will generate  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_net451_2018_12-24_14-01-07-176.trx  
+&nbsp;&nbsp;&nbsp;&nbsp;UnitTestProject/TestResults/results_netcoreapp20_2018-12-24_14-01-08-111.trx