diff --git a/modhex.go b/modhex.go
index 92cfdc1..74e15e6 100644
--- a/modhex.go
+++ b/modhex.go
@@ -67,6 +67,18 @@ func DecodedLen(n int) int {
 	return n / 2
 }
 
+// ErrLength reports an attempt to decode an odd-length input using Decode
+// or DecodeString.
+var ErrLength = errors.New("modhex: odd length modhex string")
+
+// InvalidByteError values describe errors resulting from an invalid byte in a
+// hex string.
+type InvalidByteError byte
+
+func (e InvalidByteError) Error() string {
+	return fmt.Sprintf("modhex: invalid byte: %#U", rune(e))
+}
+
 // Decode decodes src into DecodedLen(len(src)) bytes, returning
 // the actual number of bytes written to dst.
 //
@@ -78,12 +90,12 @@ func Decode(dst, src []byte) (int, error) {
 	for ; j < len(src); j += 2 {
 		a, ok := modhexMap[src[j-1]]
 		if !ok {
-			return i, fmt.Errorf("modhex: invalid byte: %#U", rune(src[j-1]))
+			return i, InvalidByteError(src[j-1])
 		}
 
 		b, ok := modhexMap[src[j]]
 		if !ok {
-			return i, fmt.Errorf("modhex: invalid byte: %#U", rune(src[j]))
+			return i, InvalidByteError(src[j])
 		}
 
 		dst[i] = (a << 4) | b
@@ -92,10 +104,10 @@ func Decode(dst, src []byte) (int, error) {
 
 	if len(src)%2 == 1 {
 		if _, ok := modhexMap[src[j-1]]; !ok {
-			return i, fmt.Errorf("modhex: invalid byte: %#U", rune(src[j-1]))
+			return i, InvalidByteError(src[j-1])
 		}
 
-		return i, errors.New("modhex: odd length modhex string")
+		return i, ErrLength
 	}
 
 	return i, nil
diff --git a/modhex_test.go b/modhex_test.go
index f3a877a..edcd96f 100644
--- a/modhex_test.go
+++ b/modhex_test.go
@@ -1,60 +1,89 @@
 package modhex
 
 import (
-	"encoding/hex"
-	"strings"
+	"bytes"
 	"testing"
 )
 
-type test struct {
-	hex    string
-	modhex string
+type encDecTest struct {
+	enc string
+	dec []byte
 }
 
-func TestEncodeHexDecodeHex(t *testing.T) {
-	var tests = []test{
-		{
-			modhex: "dteffuje",
-			hex:    "2d344e83",
-		},
-
-		{
-			modhex: "DTEFFUJE",
-			hex:    "2d344e83",
-		},
-
-		{
-			modhex: "dTeFfUjE",
-			hex:    "2d344e83",
-		},
-
-		{
-			modhex: "hknhfjbrjnlnldnhcujvddbikngjrtgh",
-			hex:    "69b6481c8baba2b60e8f22179b58cd56",
-		},
-
-		{
-			modhex: "urtubjtnuihvntcreeeecvbregfjibtn",
-			hex:    "ecde18dbe76fbd0c33330f1c354871db",
-		},
+var encDecTests = []encDecTest{
+	{"", []byte{}},
+	{"dteffuje", []byte{0x2d, 0x34, 0x4e, 0x83}},
+	{
+		"hknhfjbrjnlnldnhcujvddbikngjrtgh",
+		[]byte{0x69, 0xb6, 0x48, 0x1c, 0x8b, 0xab,
+			0xa2, 0xb6, 0x0e, 0x8f, 0x22, 0x17,
+			0x9b, 0x58, 0xcd, 0x56},
+	},
+	{
+		"urtubjtnuihvntcreeeecvbregfjibtn",
+		[]byte{0xec, 0xde, 0x18, 0xdb, 0xe7, 0x6f,
+			0xbd, 0x0c, 0x33, 0x33, 0x0f, 0x1c,
+			0x35, 0x48, 0x71, 0xdb},
+	},
+}
+
+func TestEncode(t *testing.T) {
+	for i, test := range encDecTests {
+		dst := make([]byte, EncodedLen(len(test.dec)))
+
+		n := Encode(dst, test.dec)
+
+		if n != len(dst) {
+			t.Errorf("#%d: bad return value: got %d want: %d", i, n, len(dst))
+		}
+
+		if string(dst) != test.enc {
+			t.Errorf("#%d: got: %#v want %#v", i, dst, []byte(test.enc))
+		}
 	}
+}
+
+func TestDecode(t *testing.T) {
+	for i, test := range encDecTests {
+		dst := make([]byte, DecodedLen(len(test.enc)))
 
-	for _, tc := range tests {
-		src, _ := hex.DecodeString(tc.hex)
-		modhex := EncodeToString(src)
+		n, err := Decode(dst, []byte(test.enc))
 
-		if modhex != strings.ToLower(modhex) {
-			t.Errorf("Encode Incorrect: Actual: %s; Expected: %s\n", modhex, tc.modhex)
+		if err != nil {
+			t.Errorf("#%d: unexpected err value: %s", i, err)
+			continue
 		}
 
-		hexBytes, err := DecodeString(tc.modhex)
+		if n != len(dst) {
+			t.Errorf("#%d: bad return value got: %d want:%d", i, n, len(dst))
+		}
+
+		if !bytes.Equal(dst, test.dec) {
+			t.Errorf("#%d: got %#v want: %#v", i, dst, test.dec)
+		}
+	}
+}
+
+func TestEncodeToString(t *testing.T) {
+	for i, test := range encDecTests {
+		s := EncodeToString(test.dec)
+		if s != test.enc {
+			t.Errorf("#%d: got: %s want: %s", i, s, test.enc)
+		}
+	}
+}
+
+func TestDecodeString(t *testing.T) {
+	for i, test := range encDecTests {
+		dst, err := DecodeString(test.enc)
+
 		if err != nil {
-			t.Error(err)
+			t.Errorf("#%d: unexpected err value: %s", i, err)
+			continue
 		}
 
-		hexStr := hex.EncodeToString(hexBytes)
-		if hexStr != tc.hex {
-			t.Errorf("Decode Incorrect: Actual: %s; Expected: %s\n", hexStr, tc.hex)
+		if !bytes.Equal(dst, test.dec) {
+			t.Errorf("#%d: got %#v want: %#v", i, dst, test.dec)
 		}
 	}
 }