p2p: add test for pqueue dequeue full error (#6760)

This adds a test for closing the `pqueue` while the `pqueue` contains data that has not yet been dequeued.

This issue was found while debugging #6705 

This test will fail until @cmwaters fix for this condition is merged.

internal/p2p/pqueue_test.go

@@ -0,0 +1,39 @@
+package p2p
+
+import (
+	"testing"
+	"time"
+
+	"github.com/tendermint/tendermint/libs/log"
+)
+
+func TestCloseWhileDequeueFull(t *testing.T) {
+	enqueueLength := 5
+	chDescs := []ChannelDescriptor{
+		{ID: 0x01, Priority: 1, MaxSendBytes: 4},
+	}
+	pqueue := newPQScheduler(log.NewNopLogger(), NopMetrics(), chDescs, uint(enqueueLength), 1, 120)
+
+	for i := 0; i < enqueueLength; i++ {
+		pqueue.enqueue() <- Envelope{
+			channelID: 0x01,
+			Message:   &testMessage{Value: "foo"}, // 5 bytes
+		}
+	}
+
+	go pqueue.process()
+
+	// sleep to allow context switch for process() to run
+	time.Sleep(10 * time.Millisecond)
+	doneCh := make(chan struct{})
+	go func() {
+		pqueue.close()
+		close(doneCh)
+	}()
+
+	select {
+	case <-doneCh:
+	case <-time.After(2 * time.Second):
+		t.Fatal("pqueue failed to close")
+	}
+}