Azure Pipelines locates test dll's, but is unable to execute them

Question

Problem
After hours of searching, I'm unable to find the root cause of Azure Pipelines failing to execute my various unit tests. These tests build and run locally with no warnings or issues, but will not run within my Azure Pipeline. I've seen many similar issues, but the vast majority of them regard Pipelines failing to find the test dll's in the first place (often due to an incorrect test name pattern). However, this is not the case with my situation. Pipelines has no problem locating the dll's, and even lists each one by name. Pipelines then fails to execute any of the tests in these dll's and throws an error that will be detailed in the full output below.

Full Output

   ##[section]Starting: Unit Tests  
     
   ==============================================================================  
     
   Task         : Visual Studio Test  
   Description  : Run unit and functional tests (Selenium, Appium, Coded UI test, etc.) using the Visual Studio Test (VsTest) runner. Test frameworks that have a Visual Studio test adapter such as MsTest, xUnit, NUnit, Chutzpah (for JavaScript tests using QUnit, Mocha and Jasmine), etc. can be run. Tests can be distributed on multiple agents using this task (version 2).  
   Version      : 2.153.9  
   Author       : Microsoft Corporation  
   Help         : https://learn.microsoft.com/azure/devops/pipelines/tasks/test/vstest  
     
   ==============================================================================  
     
   SystemVssConnection exists true  
   ##[warning]Unable to get feature flag: TestExecution.EnableHydra  
   SystemVssConnection exists true  
   ##[warning]Unable to get feature flag: TestExecution.EnableTranslationApi  
   SystemVssConnection exists true  
   ##[warning]Unable to get feature flag: TestExecution.EnableDiagnostics  
   Running tests using vstest.console.exe runner.  
     
   ======================================================  
     
   Test selector : Test assemblies  
   Test filter criteria : null  
   Search folder : C:\agent\_work\34\s  
   VisualStudio version selected for test execution : latest  
   Attempting to find vstest.console from a visual studio installation.  
   Run in parallel : false  
   Run in isolation : false  
   Path to custom adapters : null  
   Other console options : null  
   Code coverage enabled : true  
   Diagnostics enabled : false  
   SystemVssConnection exists true  
   Run the tests locally using vstest.console.exe  
     
   ========================================================  
     
   Test selector : Test assemblies  
   Test assemblies : **\release\**\*UnitTests.dll,**\release\**\**\*UnitTests.dll,!**\obj\**  
   Test filter criteria : null  
   Search folder : C:\agent\_work\34\s  
   Run settings file : C:\agent\_work\34\s  
   Run in parallel : false  
   Run in isolation : false  
   Path to custom adapters : null  
   Other console options : null  
   Code coverage enabled : true  
   Diagnostics enabled : false  
   Rerun failed tests: false  
   VisualStudio version selected for test execution : latest  
   Attempting to find vstest.console from a visual studio installation.  
     
   ========================================================  
     
     
   ======================================================  
     
   [command]"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\Common7\IDE\Extensions\TestPlatform\vstest.console.exe" @C:\agent\_work\_temp\2c095351-b2dc-11eb-b929-bff4d6da517a.txt  
   Microsoft (R) Test Execution Command Line Tool Version 16.7.0  
   Copyright (c) Microsoft Corporation.  All rights reserved.  
     
   vstest.console.exe   
   "C:\agent\_work\34\s\Source\bin\Release\Service1.UnitTests\Service1.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service2.UnitTests\Company.Service2.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service3.UnitTests\Service3.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service4.UnitTests\Company.Service4.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service5.UnitTests\Company.Service5.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service6.UnitTests\Company.Service6.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service7.UnitTests\Company.Service7.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service8.UnitTests\Company.Service8.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service9.UnitTests\Company.Service9.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Company.Service10.UnitTests\Company.Product.Service10.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Company.Service11.UnitTests\Company.Service11.UnitTests.dll"  
   "C:\agent\_work\34\s\Source\bin\Release\Service12\Company.Service9.UnitTests.dll"  
   /EnableCodeCoverage  
   /logger:"trx"  
   /TestAdapterPath:"C:\agent\_work\34\s"  
   Starting test execution, please wait...  
   M i c r o s o f t   ( R )   C o v e r a g e   C o l l e c t i o n   T o o l   V e r s i o n   1 6 . 0 . 3 0 3 1 9 . 2 0 0   
      
      
    C o p y r i g h t   ( c )   M i c r o s o f t   C o r p o r a t i o n .     A l l   r i g h t s   r e s e r v e d .   
      
      
      
      
    2.6157  
     
   A total of 12 test files matched the specified pattern.  
   No test is available in C:\agent\_work\34\s\Source\bin\Release\Service1.UnitTests\Service1.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service2.UnitTests\Company.Service2.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service3.UnitTests\Service3.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service4.UnitTests\Company.Service4.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service5.UnitTests\Company.Service5.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service6.UnitTests\Company.Service6.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service7.UnitTests\Company.Service7.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service8.UnitTests\Company.Service8.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service9.UnitTests\Company.Service9.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Company.Service10.UnitTests\Company.Product.Service10.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Company.Service11.UnitTests\Company.Service11.UnitTests.dll C:\agent\_work\34\s\Source\bin\Release\Service12\Company.Service9.UnitTests.dll. Make sure that test discoverer & executors are registered and platform & framework version settings are appropriate and try again.  
   M i c r o s o f t   ( R )   C o v e r a g e   C o l l e c t i o n   T o o l   V e r s i o n   1 6 . 0 . 3 0 3 1 9 . 2 0 0   
      
      
    C o p y r i g h t   ( c )   M i c r o s o f t   C o r p o r a t i o n .     A l l   r i g h t s   r e s e r v e d .   
      
      
      
      
    Results File: C:\agent\_work\34\s\TestResults\result.trx  
     
   Attachments:  
     C:\agent\_work\34\s\TestResults\result_coverage.coverage  
   No Result Found to Publish 'C:\agent\_work\34\s\TestResults\result.trx'.  
   ##[section]Async Command Start: Publish test results  
   ##[section]Async Command End: Publish test results  
   ##[section]Finishing: Unit Tests  

Answer 1

Devops / TFS is not currently supported here on QnA. The product group for Azure DevOps / TFS actively monitors questions over at
https://developercommunity.visualstudio.com/report?space=21&entry=problem
https://developercommunity.visualstudio.com/report?space=22&entry=problem

--please don't forget to Accept as answer if the reply is helpful--