diff --git a/apduWrapper.go b/apduWrapper.go
index 49d6ab2..4e46353 100644
--- a/apduWrapper.go
+++ b/apduWrapper.go
@@ -30,11 +30,18 @@ const (
 
 var codec = binary.BigEndian
 
+const (
+	ErrMsgPacketSize       = "packet size must be at least 3"
+	ErrMsgInvalidChannel   = "invalid channel"
+	ErrMsgInvalidTag       = "invalid tag"
+	ErrMsgWrongSequenceIdx = "wrong sequenceIdx"
+)
+
 var (
-	ErrPacketSize       = errors.New("packet size must be at least 3")
-	ErrInvalidChannel   = errors.New("invalid channel")
-	ErrInvalidTag       = errors.New("invalid tag")
-	ErrWrongSequenceIdx = errors.New("wrong sequenceIdx")
+	ErrPacketSize       = errors.New(ErrMsgPacketSize)
+	ErrInvalidChannel   = errors.New(ErrMsgInvalidChannel)
+	ErrInvalidTag       = errors.New(ErrMsgInvalidTag)
+	ErrWrongSequenceIdx = errors.New(ErrMsgWrongSequenceIdx)
 )
 
 // ErrorMessage returns a human-readable error message for a given APDU error code.
diff --git a/ledger.go b/ledger.go
index 02563ef..28df9a4 100644
--- a/ledger.go
+++ b/ledger.go
@@ -16,12 +16,14 @@
 
 package ledger_go
 
+// LedgerAdmin defines the interface for managing Ledger devices.
 type LedgerAdmin interface {
 	CountDevices() int
 	ListDevices() ([]string, error)
 	Connect(deviceIndex int) (LedgerDevice, error)
 }
 
+// LedgerDevice defines the interface for interacting with a Ledger device.
 type LedgerDevice interface {
 	Exchange(command []byte) ([]byte, error)
 	Close() error
diff --git a/ledger_hid.go b/ledger_hid.go
index f8f83d7..7718479 100644
--- a/ledger_hid.go
+++ b/ledger_hid.go
@@ -59,27 +59,30 @@ func NewLedgerAdmin() *LedgerAdminHID {
 
 func (admin *LedgerAdminHID) ListDevices() ([]string, error) {
 	devices := hid.Enumerate(0, 0)
-
 	if len(devices) == 0 {
-		fmt.Printf("No devices. Ledger LOCKED OR Other Program/Web Browser may have control of device.")
+		log.Println("No devices. Ledger LOCKED OR Other Program/Web Browser may have control of device.")
 	}
 
 	for _, d := range devices {
-		fmt.Printf("============ %s\n", d.Path)
-		fmt.Printf("VendorID      : %x\n", d.VendorID)
-		fmt.Printf("ProductID     : %x\n", d.ProductID)
-		fmt.Printf("Release       : %x\n", d.Release)
-		fmt.Printf("Serial        : %x\n", d.Serial)
-		fmt.Printf("Manufacturer  : %s\n", d.Manufacturer)
-		fmt.Printf("Product       : %s\n", d.Product)
-		fmt.Printf("UsagePage     : %x\n", d.UsagePage)
-		fmt.Printf("Usage         : %x\n", d.Usage)
-		fmt.Printf("\n")
+		logDeviceInfo(d)
 	}
 
 	return []string{}, nil
 }
 
+func logDeviceInfo(d hid.DeviceInfo) {
+	log.Printf("============ %s\n", d.Path)
+	log.Printf("VendorID      : %x\n", d.VendorID)
+	log.Printf("ProductID     : %x\n", d.ProductID)
+	log.Printf("Release       : %x\n", d.Release)
+	log.Printf("Serial        : %x\n", d.Serial)
+	log.Printf("Manufacturer  : %s\n", d.Manufacturer)
+	log.Printf("Product       : %s\n", d.Product)
+	log.Printf("UsagePage     : %x\n", d.UsagePage)
+	log.Printf("Usage         : %x\n", d.Usage)
+	log.Printf("\n")
+}
+
 func isLedgerDevice(d hid.DeviceInfo) bool {
 	deviceFound := d.UsagePage == UsagePageLedgerNanoS
 	// Workarounds for possible empty usage pages
diff --git a/ledger_mock.go b/ledger_mock.go
index a16eb10..af1857f 100644
--- a/ledger_mock.go
+++ b/ledger_mock.go
@@ -24,10 +24,12 @@ import (
 	"fmt"
 )
 
+const mockDeviceName = "Mock device"
+
 type LedgerAdminMock struct{}
 
 type LedgerDeviceMock struct {
-	commands map[string][]byte
+	commands map[string]string
 }
 
 func NewLedgerAdmin() *LedgerAdminMock {
@@ -35,8 +37,7 @@ func NewLedgerAdmin() *LedgerAdminMock {
 }
 
 func (admin *LedgerAdminMock) ListDevices() ([]string, error) {
-	x := []string{"Mock device"}
-	return x, nil
+	return []string{mockDeviceName}, nil
 }
 
 func (admin *LedgerAdminMock) CountDevices() int {
@@ -49,8 +50,8 @@ func (admin *LedgerAdminMock) Connect(deviceIndex int) (*LedgerDeviceMock, error
 
 func NewLedgerDeviceMock() *LedgerDeviceMock {
 	return &LedgerDeviceMock{
-		commands: map[string][]byte{
-			"e001000000": []byte{0x31, 0x10, 0x00, 0x04, 0x08, 0x53, 0x70, 0x65, 0x63, 0x75, 0x6c, 0x6f, 0x73, 0x00, 0x0b, 0x53, 0x70, 0x65, 0x63, 0x75, 0x6c, 0x6f, 0x73, 0x4d, 0x43, 0x55},
+		commands: map[string]string{
+			"e001000000": "311000040853706563756c6f73000b53706563756c6f734d4355",
 		},
 	}
 }
@@ -58,7 +59,7 @@ func NewLedgerDeviceMock() *LedgerDeviceMock {
 func (ledger *LedgerDeviceMock) Exchange(command []byte) ([]byte, error) {
 	hexCommand := hex.EncodeToString(command)
 	if reply, ok := ledger.commands[hexCommand]; ok {
-		return reply, nil
+		return hex.DecodeString(reply)
 	}
 	return nil, fmt.Errorf("unknown command: %s", hexCommand)
 }
diff --git a/ledger_test.go b/ledger_test.go
index a117864..6f99623 100644
--- a/ledger_test.go
+++ b/ledger_test.go
@@ -27,13 +27,31 @@ import (
 
 var mux sync.Mutex
 
+func TestLedger(t *testing.T) {
+	tests := []struct {
+		name string
+		test func(t *testing.T)
+	}{
+		{"CountLedgerDevices", Test_CountLedgerDevices},
+		{"ListDevices", TestListDevices},
+		{"GetLedger", Test_GetLedger},
+		{"BasicExchange", Test_BasicExchange},
+		{"Connect", TestConnect},
+		{"GetVersion", TestGetVersion},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, tt.test)
+	}
+}
+
 func Test_CountLedgerDevices(t *testing.T) {
 	mux.Lock()
 	defer mux.Unlock()
 
 	ledgerAdmin := NewLedgerAdmin()
 	count := ledgerAdmin.CountDevices()
-	assert.True(t, count > 0)
+	require.True(t, count > 0)
 }
 
 func TestListDevices(t *testing.T) {
@@ -121,4 +139,4 @@ func TestGetVersion(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotEmpty(t, response, "Response should not be empty")
 
-}
\ No newline at end of file
+}
diff --git a/ledger_zemu.go b/ledger_zemu.go
index 5a5183c..db8a026 100644
--- a/ledger_zemu.go
+++ b/ledger_zemu.go
@@ -27,6 +27,11 @@ import (
 	"google.golang.org/grpc"
 )
 
+const (
+	defaultGrpcURL  = "localhost"
+	defaultGrpcPort = "3002"
+)
+
 type LedgerAdminZemu struct {
 	grpcURL  string
 	grpcPort string
@@ -39,9 +44,8 @@ type LedgerDeviceZemu struct {
 
 func NewLedgerAdmin() *LedgerAdminZemu {
 	return &LedgerAdminZemu{
-		//TODO get this from flag value or from Zemu response
-		grpcURL:  "localhost",
-		grpcPort: "3002",
+		grpcURL:  defaultGrpcURL,
+		grpcPort: defaultGrpcPort,
 	}
 }