Unexpected overhead in test execution times when the number of test cases increases

Description

Unexpected overhead in test execution times when the number of test cases increases. The increase is non-linear with the increase in number of tests.

Execute a test run with one assembly containing 10k test cases => Takes ~ 10.65s
Execute a test run with one assembly containing 50k test cases => Takes ~ 165.87s

[Execute a test run with five assemblies each containing 10k test cases => Takes ~ 50.1s]

It should take around 50s for the second case

Is this represented in the perf workloads we use? If so, is this a regression?

There are still multiple performance issues with MSTest but this issue as-is is not really actionable so I will close it.