Pipe protocol: The design of InstanceId

[Youssef1313]

Today, we recognize retries by receiving a different "instance id". A new "instance id" essentially means "this is a different test host".

testfx/src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/DotnetTestConnection.cs

Line 29 in a2f4caf

public static string InstanceId { get; } = Guid.NewGuid().ToString("N");

This feels like an incomplete design to me. What if we want to support batching. Are we going to have an env variable that takes precedence over Guid.NewGuid().ToString("N")?

Long-term, I think it's more wise to encode the information about "attempt number" inside the protocol. So, each test result is received with an "attempt number" in case of retries. But that might not be easy to change "now", probably.

[Youssef1313]

cc @mariam-abdulla