rewrite unmarshaling interface and tests of formats (#238)

pkg/formats/lpcm_test.go

@@ -1,8 +1,6 @@
 package formats
 
 import (
-	"fmt"
-	"strconv"
 	"testing"
 
 	"github.com/pion/rtp"
@@ -22,23 +20,6 @@ func TestLPCMAttributes(t *testing.T) {
 	require.Equal(t, true, format.PTSEqualsDTS(&rtp.Packet{}))
 }
 
-func TestLPCMMediaDescription(t *testing.T) {
-	for _, ca := range []int{8, 16, 24} {
-		t.Run(strconv.FormatInt(int64(ca), 10), func(t *testing.T) {
-			format := &LPCM{
-				PayloadTyp:   96,
-				BitDepth:     ca,
-				SampleRate:   96000,
-				ChannelCount: 2,
-			}
-
-			rtpmap, fmtp := format.Marshal()
-			require.Equal(t, fmt.Sprintf("L%d/96000/2", ca), rtpmap)
-			require.Equal(t, map[string]string(nil), fmtp)
-		})
-	}
-}
-
 func TestLPCMDecEncoder(t *testing.T) {
 	format := &LPCM{
 		PayloadTyp:   96,