add test coverage

Signed-off-by: Bryce Kahle <bryce.kahle@datadoghq.com>

perf/reader_test.go

@@ -38,9 +38,15 @@ func TestPerfReader(t *testing.T) {
 	}
 	defer rd.Close()
 
-	outputSamples(t, events, 5)
+	qt.Assert(t, rd.Size(), qt.Equals, 4096)
 
-	checkRecord(t, rd)
+	outputSamples(t, events, 5, 5)
+
+	_, rem := checkRecord(t, rd)
+	qt.Assert(t, rem >= 5, qt.IsTrue, qt.Commentf("expected at least 5 Remaining"))
+
+	_, rem = checkRecord(t, rd)
+	qt.Assert(t, rem, qt.Equals, 0, qt.Commentf("expected zero Remaining"))
 
 	rd.SetDeadline(time.Now().Add(4 * time.Millisecond))
 	_, err = rd.Read()
@@ -155,7 +161,7 @@ func outputSamplesProg(tb testing.TB, events *ebpf.Map, sampleSizes ...byte) *eb
 	return prog
 }
 
-func checkRecord(tb testing.TB, rd *Reader) (id int) {
+func checkRecord(tb testing.TB, rd *Reader) (id int, remaining int) {
 	tb.Helper()
 
 	rec, err := rd.Read()
@@ -172,7 +178,7 @@ func checkRecord(tb testing.TB, rd *Reader) (id int) {
 
 	// padding is ignored since it's value is undefined.
 
-	return int(rec.RawSample[1])
+	return int(rec.RawSample[1]), rec.Remaining
 }
 
 func TestPerfReaderLostSample(t *testing.T) {
@@ -305,8 +311,13 @@ func TestPerfReaderOverwritable(t *testing.T) {
 
 	nextID := maxEvents
 	for i := 0; i < maxEvents; i++ {
-		id := checkRecord(t, rd)
+		id, rem := checkRecord(t, rd)
 		qt.Assert(t, id, qt.Equals, nextID)
+		if i < maxEvents-1 {
+			qt.Assert(t, rem > 0, qt.IsTrue, qt.Commentf("expected non-zero Remaining"))
+		} else {
+			// remaining can be zero or non-zero, depending on if the buffer has been overwritten
+		}
 		nextID--
 	}
 }

ringbuf/reader_test.go

@@ -59,6 +59,10 @@ func TestRingbufReader(t *testing.T) {
 			}
 			defer rd.Close()
 
+			if uint32(rd.Size()) != 2*events.MaxEntries() {
+				t.Errorf("expected %d Size, got %d", events.MaxEntries(), rd.Size())
+			}
+
 			ret, _, err := prog.Test(internal.EmptyBPFContext)
 			testutils.SkipIfNotSupported(t, err)
 			if err != nil {
@@ -77,6 +81,15 @@ func TestRingbufReader(t *testing.T) {
 					t.Fatal("Can't read samples:", err)
 				}
 				raw[len(record.RawSample)] = record.RawSample
+				if len(raw) == len(tt.want) {
+					if record.Remaining != 0 {
+						t.Errorf("expected 0 Remaining, got %d", record.Remaining)
+					}
+				} else {
+					if record.Remaining == 0 {
+						t.Error("expected non-zero Remaining, got 0")
+					}
+				}
 			}
 
 			if diff := cmp.Diff(tt.want, raw); diff != "" {