Fix test checking idToTrace map used in tail sampling (#486)

The test seems to have been running in sequence on most (all?) of Travis runs: it makes assumptions about which traces will be present on idToTrace map and that is not possible when traces are added concurrently since there are no guarantees about the insertion order.

Fixed the concurrent test and added a sequential test in which the ids that are expected to have been dropped can be actually validated.

Author: Paulo Janotti

internal/collector/processor/tailsampling/processor_test.go

@@ -84,9 +84,26 @@ func TestConcurrentTraceArrival(t *testing.T) {
 	}
 }
 
-func TestConcurrentTraceMapSize(t *testing.T) {
+func TestSequentialTraceMapSize(t *testing.T) {
 	traceIds, batches := generateIdsAndBatches(210)
 	const maxSize = 100
+	sp, _ := NewTailSamplingSpanProcessor(newTestPolicy(), uint64(maxSize), 64, defaultTestDecisionWait, zap.NewNop())
+	tsp := sp.(*tailSamplingSpanProcessor)
+	for _, batch := range batches {
+		tsp.ProcessSpans(batch, "test")
+	}
+
+	// On sequential insertion it is possible to know exactly which traces should be still on the map.
+	for i := 0; i < len(traceIds)-maxSize; i++ {
+		if _, ok := tsp.idToTrace.Load(traceKey(traceIds[i])); ok {
+			t.Fatalf("Found unexpected traceId[%d] still on map (id: %v)", i, traceIds[i])
+		}
+	}
+}
+
+func TestConcurrentTraceMapSize(t *testing.T) {
+	_, batches := generateIdsAndBatches(210)
+	const maxSize = 100
 	var wg sync.WaitGroup
 	sp, _ := NewTailSamplingSpanProcessor(newTestPolicy(), uint64(maxSize), 64, defaultTestDecisionWait, zap.NewNop())
 	tsp := sp.(*tailSamplingSpanProcessor)
@@ -100,10 +117,15 @@ func TestConcurrentTraceMapSize(t *testing.T) {
 
 	wg.Wait()
 
-	for i := 0; i < len(traceIds)-maxSize; i++ {
-		if _, ok := tsp.idToTrace.Load(traceKey(traceIds[i])); ok {
-			t.Fatalf("Found unexpected traceId[%d] still on map (id: %v)", i, traceIds[i])
-		}
+	// Since we can't guarantee the order of insertion the only thing that can be checked is
+	// if the number of traces on the map matches the expected value.
+	cnt := 0
+	tsp.idToTrace.Range(func(_ interface{}, _ interface{}) bool {
+		cnt++
+		return true
+	})
+	if cnt != maxSize {
+		t.Fatalf("got %d traces on idToTrace, want %d", cnt, maxSize)
 	}
 }