diff --git a/helper/hex/hex.go b/helper/hex/hex.go
index 7ab38d903d..8a61a17c83 100644
--- a/helper/hex/hex.go
+++ b/helper/hex/hex.go
@@ -8,10 +8,6 @@ import (
 	"strings"
 )
 
-type DecError struct{ msg string }
-
-func (err DecError) Error() string { return err.msg }
-
 // EncodeToHex generates a hex string based on the byte representation, with the '0x' prefix
 func EncodeToHex(str []byte) string {
 	return "0x" + hex.EncodeToString(str)
@@ -60,22 +56,6 @@ func DecodeUint64(hexStr string) (uint64, error) {
 	return strconv.ParseUint(cleaned, 16, 64)
 }
 
-const BadNibble = ^uint64(0)
-
-// DecodeNibble decodes a byte into a uint64
-func DecodeNibble(in byte) uint64 {
-	switch {
-	case in >= '0' && in <= '9':
-		return uint64(in - '0')
-	case in >= 'A' && in <= 'F':
-		return uint64(in - 'A' + 10)
-	case in >= 'a' && in <= 'f':
-		return uint64(in - 'a' + 10)
-	default:
-		return BadNibble
-	}
-}
-
 // EncodeBig encodes bigint as a hex string with 0x prefix.
 // The sign of the integer is ignored.
 func EncodeBig(bigint *big.Int) string {
diff --git a/helper/hex/hex_test.go b/helper/hex/hex_test.go
index 9717281fa6..01d27ca930 100644
--- a/helper/hex/hex_test.go
+++ b/helper/hex/hex_test.go
@@ -2,6 +2,7 @@ package hex
 
 import (
 	"fmt"
+	"math/big"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -67,3 +68,139 @@ func TestDecodeHexToBig(t *testing.T) {
 		require.Equal(t, uint64(512), big.Uint64())
 	})
 }
+
+func TestEncodeToHex(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    []byte
+		expected string
+	}{
+		{[]byte{}, "0x"},
+		{[]byte{0x00}, "0x00"},
+		{[]byte{0x01}, "0x01"},
+		{[]byte{0x0A, 0x0B, 0x0C}, "0x0a0b0c"},
+		{[]byte{0xFF, 0xFE, 0xFD}, "0xfffefd"},
+	}
+
+	for _, tc := range testCases {
+		actual := EncodeToHex(tc.input)
+		assert.Equal(t, tc.expected, actual)
+	}
+}
+
+func TestEncodeToString(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    []byte
+		expected string
+	}{
+		{[]byte{}, ""},
+		{[]byte{0x00}, "00"},
+		{[]byte{0x01}, "01"},
+		{[]byte{0x0A, 0x0B, 0x0C}, "0a0b0c"},
+		{[]byte{0xFF, 0xFE, 0xFD}, "fffefd"},
+	}
+
+	for _, tc := range testCases {
+		actual := EncodeToString(tc.input)
+		assert.Equal(t, tc.expected, actual)
+	}
+}
+
+func TestMustDecodeHex(t *testing.T) {
+	t.Parallel()
+
+	t.Run("Valid hex string", func(t *testing.T) {
+		t.Parallel()
+
+		str := "0x48656c6c6f20576f726c64"
+		expected := []byte{0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64}
+
+		actual := MustDecodeHex(str)
+		assert.Equal(t, expected, actual)
+	})
+
+	t.Run("Empty hex string", func(t *testing.T) {
+		t.Parallel()
+
+		str := ""
+		expected := []byte{}
+
+		actual := MustDecodeHex(str)
+		assert.Equal(t, expected, actual)
+	})
+
+	t.Run("Invalid hex string", func(t *testing.T) {
+		t.Parallel()
+
+		str := "0x12345q"
+
+		require.PanicsWithError(t, "could not decode hex: encoding/hex: invalid byte: U+0071 'q'", func() {
+			MustDecodeHex(str)
+		})
+	})
+}
+
+func TestEncodeUint64(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    uint64
+		expected string
+	}{
+		{0, "0x0"},
+		{1, "0x1"},
+		{11, "0xb"},
+		{67312, "0x106f0"},
+		{80604, "0x13adc"},
+		{^uint64(0), "0xffffffffffffffff"}, // max uint64
+	}
+
+	for _, tc := range testCases {
+		actual := EncodeUint64(tc.input)
+		assert.Equal(t, tc.expected, actual)
+	}
+}
+
+func TestEncodeBig(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    *big.Int
+		expected string
+	}{
+		{big.NewInt(0), "0x0"},
+		{big.NewInt(1), "0x1"},
+		{big.NewInt(11), "0xb"},
+		{big.NewInt(67312), "0x106f0"},
+		{big.NewInt(80604), "0x13adc"},
+		{new(big.Int).SetUint64(^uint64(0)), "0xffffffffffffffff"}, // max uint64
+	}
+
+	for _, tc := range testCases {
+		actual := EncodeBig(tc.input)
+		assert.Equal(t, tc.expected, actual)
+	}
+}
+
+func TestDecodeString(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    string
+		expected []byte
+	}{
+		{"", []byte{}},
+		{"48656c6c6f20576f726c64", []byte{0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64}},
+		{"0123456789abcdef", []byte{0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef}},
+		{"fffe", []byte{0xff, 0xfe}},
+	}
+
+	for _, tc := range testCases {
+		actual, err := DecodeString(tc.input)
+		assert.NoError(t, err)
+		assert.Equal(t, tc.expected, actual)
+	}
+}