Another thing, i took the config file from my PC - where the tests are flying - and put it on the build server.
This is my conf file:
<GlobalConfiguration>
<Settings>
<CPUCoresAssignedToNCrunch>0,1,2,3,4,5,6,7,8,9,10,11,12,13</CPUCoresAssignedToNCrunch>
<CPUCoresAssignedToVisualStudio>14,15,16,17,18,19,20,21,22,23,24,25,26,27</CPUCoresAssignedToVisualStudio>
<FastLaneThreads>1</FastLaneThreads>
<MaxNumberOfProcessingThreads>14</MaxNumberOfProcessingThreads>
<MaxTestRunnerProcessesToPool>1</MaxTestRunnerProcessesToPool>
<SystemConfigured>True</SystemConfigured>
<TerminateTestRunnerTasksOnExecutionComplete>False</TerminateTestRunnerTasksOnExecutionComplete>
<UseSimplifiedSettingsWhereAvailable>True</UseSimplifiedSettingsWhereAvailable>
<WizardAllowParallelTestExecution>True</WizardAllowParallelTestExecution>
<WizardEngineMode>Run all tests automatically</WizardEngineMode>
<WizardIgnoreTests>False</WizardIgnoreTests>
</Settings>
<EngineModes>
<EngineMode>
<Name>Run all tests automatically</Name>
<Settings />
</EngineMode>
<EngineMode>
<Name>Run all tests manually</Name>
<Settings>
<TestsToExecuteAutomatically>False</TestsToExecuteAutomatically>
</Settings>
</EngineMode>
<EngineMode>
<Name>Run impacted tests automatically, others manually</Name>
<Settings>
<AlignOutOfDateStatusWithImpactStatus>True</AlignOutOfDateStatusWithImpactStatus>
<TestsToExecuteAutomatically>IsImpacted</TestsToExecuteAutomatically>
</Settings>
</EngineMode>
<EngineMode>
<Name>Run pinned tests automatically, others manually</Name>
<Settings>
<AutoPinNewTests>True</AutoPinNewTests>
<TestsToExecuteAutomatically>IsPinned</TestsToExecuteAutomatically>
</Settings>
</EngineMode>
</EngineModes>
</GlobalConfiguration>
i also tried to change the FastLaneThreads to 0, MaxTestRunnerProcessesToPool to 10 and remove the CPUCoresAssignedToNCrunch & CPUCoresAssignedToVisualStudio.
i see that i have only one or two TestHost processes that are working - all the rest are with CPU 0, whereas on my computer i have about 14 or 15 that are working hard.