Runtime: Fill in test gaps for Event Pipe

[tommcdon]

We need to add new tests to cover .net core 3.0 event pipe test scenarios. These new tests will supercede the following:

• [ ] https://github.com/dotnet/coreclr/issues/23224
• [ ] https://github.com/dotnet/coreclr/issues/22891
• [ ] https://github.com/dotnet/coreclr/issues/20510
• [ ] https://github.com/dotnet/coreclr/issues/20299

[josalem]

Do we have a list of scenarios we want to prioritize? I have a template for writing the tests that we can use to _hopefully_ iterate quickly through them.

[tommcdon]

Let's use this issue to track the sceanrios we wish to fill
@cshung @sywhang

[josalem]

I believe we should add tests covering the following "knobs":

• [ ] Messages sent vs received under:
  
  
  
  • varying buffer sizes
  
  
  • varying providers
  
  
• [ ] Provider turned on vs sane traces (e.g., if I trace GC, I should see equal numbers of start and end events)
  
  
  
  • varying buffer sizes
  
  
• [ ] EventPipe Connection _and_ EventListener connection being coherent

[jorive]

@josalem Should we add to the mix:

• [ ] Verify providers/events enabled are written
• [ ] Verify CPU stacks are written when enabled
• [ ] Handle erroneous user input

[josalem]

Agreed. I think we should have a small base set of tests we can add to PR validation, and a larger, more complex set we can add to pri-1 testing. These tests give us a chance to implicitly "soft" document some guarantees about the EventPipe system that shouldn't be broken by incoming changes.

[noahfalk]

What do you guys think about promoting this list of test cases into a markdown doc that we put in the tree? Often when researching tests available in some area I'd run into two questions:
a) Is scenario X tested?
b) If it is, which of the 100 tests in this area covers it?
Typically this is looking back months/years after the tests were originally written so any issues (such as this one) aren't easily discoverable at that point.

[sywhang]

Sounds good to me.

[tommcdon]

@josalem close?

[josalem]

I think we've got decent coverage for EventPipe in the runtime repo now. There is also some md in the diagnostics repo documenting what is covered. I'm going to close this.