container/mts: added comments to tests

container/mts/mpegts_test.go

@@ -34,11 +34,14 @@ import (
 	"github.com/Comcast/gots/packet"
 )
 
+// TestBytes checks that Packet.Bytes() correctly produces a []byte
+// representation of a Packet.
 func TestBytes(t *testing.T) {
+	const payloadLen, payloadChar, stuffingChar = 120, 0x11, 0xff
+	const stuffingLen = PacketSize - payloadLen - 12
+
 	tests := []struct {
 		packet         Packet
-		payloadLen     int
-		stuffingLen    int
 		expectedHeader []byte
 	}{
 		{
@@ -51,14 +54,12 @@ func TestBytes(t *testing.T) {
 				PCRF: true,
 				PCR:  1,
 			},
-			payloadLen:  120,
-			stuffingLen: 56,
 			expectedHeader: []byte{
 				0x47,                               // Sync byte.
 				0x40,                               // TEI=0, PUSI=1, TP=0, PID=00000.
 				0x01,                               // PID(Cont)=00000001.
 				0x34,                               // TSC=00, AFC=11(adaptation followed by payload), CC=0100(4).
-				0x3f,                               // AFL=.
+				byte(7 + stuffingLen),              // AFL=.
 				0x50,                               // DI=0,RAI=1,ESPI=0,PCRF=1,OPCRF=0,SPF=0,TPDF=0, AFEF=0.
 				0x00, 0x00, 0x00, 0x00, 0x80, 0x00, // PCR.
 			},
@@ -67,26 +68,24 @@ func TestBytes(t *testing.T) {
 
 	for testNum, test := range tests {
 		// Construct payload.
-		const payloadChar = 0x11
-		payload := make([]byte, 0, test.payloadLen)
-		for i := 0; i < test.payloadLen; i++ {
+		payload := make([]byte, 0, payloadLen)
+		for i := 0; i < payloadLen; i++ {
 			payload = append(payload, payloadChar)
 		}
 
 		// Fill the packet payload.
 		test.packet.FillPayload(payload)
 
-		// Create packet data and copy in expected header.
+		// Create expected packet data and copy in expected header.
 		expected := make([]byte, len(test.expectedHeader), PacketSize)
 		copy(expected, test.expectedHeader)
 
 		// Append stuffing.
-		const stuffingChar = 0xff
-		for i := 0; i < test.stuffingLen; i++ {
+		for i := 0; i < stuffingLen; i++ {
 			expected = append(expected, stuffingChar)
 		}
 
-		// Copy in payload.
+		// Append payload to expected bytes.
 		expected = append(expected, payload...)
 
 		// Compare got with expected.
@@ -97,15 +96,19 @@ func TestBytes(t *testing.T) {
 	}
 }
 
+// TestFindPid checks that FindPid can correctly extract the first instance
+// of a PID from an MPEGTS stream.
 func TestFindPid(t *testing.T) {
 	const targetPacketNum, numOfPackets, targetPid, stdPid = 6, 15, 1, 0
 
+	// Prepare the stream of packets.
 	var stream []byte
 	for i := 0; i < numOfPackets; i++ {
 		pid := uint16(0)
 		if i == targetPacketNum {
 			pid = 1
 		}
+
 		p := Packet{
 			PID: pid,
 			AFC: hasPayload | hasAdaptationField,
@@ -114,11 +117,13 @@ func TestFindPid(t *testing.T) {
 		stream = append(stream, p.Bytes(nil)...)
 	}
 
+	// Try to find the targetPid in the stream.
 	p, i, err := FindPid(stream, targetPid)
 	if err != nil {
 		t.Fatalf("unexpected error finding PID: %v\n", err)
 	}
 
+	// Check the payload.
 	var _p packet.Packet
 	copy(_p[:], p)
 	payload, err := packet.Payload(&_p)
@@ -130,6 +135,7 @@ func TestFindPid(t *testing.T) {
 		t.Errorf("payload of found packet is not correct.\nGot: %v, Want: %v\n", got, targetPacketNum)
 	}
 
+	// Check the index.
 	_got := i / PacketSize
 	if _got != targetPacketNum {
 		t.Errorf("index of found packet is not correct.\nGot: %v, want: %v\n", _got, targetPacketNum)