Race condition between TargetIn event in StepRunner and events emission in TestStep

[rihter007]

The problem raises as we can't atomicly (at least without "ugly" locks in events emission) pass the target to the test step via channel and emit EventTargetIn event.

Currently we are having the following partial work-around:

https://github.com/linuxboot/contest/blob/main/pkg/runner/step_runner.go#L193

// put the target into step runner
case sr.input <- tgt:
// by the time we are hare, the test step could have already processed the target and emitted 100500 events
// test steps rarely emit events, so it is not a big issue. For consistency with TargetOut or TargetError I made this hack:

    // we should always emit TargetIn before TargetOut or TargetError
    // we have a race condition that outputLoop may receive result for this target first
    // in that case we will emit TargetIn in outputLoop and should not emit it here
    sr.mu.Lock()
   if targetInfo.acquireTargetInEmission() {
       if err := emitEvent(ctx, ev, target.EventTargetIn, tgt, nil); err != nil {
           sr.setErrLocked(ctx, fmt.Errorf("failed to report target injection: %w", err))
       }
    }
   sr.mu.Unlock()