diff --git a/client_handler.go b/client_handler.go
index 6d336b72..d3313295 100644
--- a/client_handler.go
+++ b/client_handler.go
@@ -360,7 +360,7 @@ func (c *clientHandler) Close() error {
 	// closing the connection from a different goroutine should be safe
 	err := c.conn.Close()
 	if err != nil {
-		err = NewNetworkError("error closing control connection", err)
+		err = newNetworkError("error closing control connection", err)
 	}
 
 	return err
@@ -650,7 +650,7 @@ func (c *clientHandler) TransferOpen(info string) (net.Conn, error) {
 
 		c.writeMessage(StatusCannotOpenDataConnection, err.Error())
 
-		err = NewNetworkError("Unable to open transfer", err)
+		err = newNetworkError("Unable to open transfer", err)
 
 		return nil, err
 	}
diff --git a/errors.go b/errors.go
index 51706f2c..6319bba5 100644
--- a/errors.go
+++ b/errors.go
@@ -31,7 +31,7 @@ type DriverError struct {
 	err error
 }
 
-func NewDriverError(str string, err error) DriverError {
+func newDriverError(str string, err error) DriverError {
 	return DriverError{str: str, err: err}
 }
 
@@ -43,12 +43,13 @@ func (e DriverError) Unwrap() error {
 	return e.err
 }
 
+// NetworkError is a wrapper for any error that occur while contacting the network
 type NetworkError struct {
 	str string
 	err error
 }
 
-func NewNetworkError(str string, err error) NetworkError {
+func newNetworkError(str string, err error) NetworkError {
 	return NetworkError{str: str, err: err}
 }
 
@@ -60,12 +61,13 @@ func (e NetworkError) Unwrap() error {
 	return e.err
 }
 
+// FileAccessError is a wrapper for any error that occur while accessing the file system
 type FileAccessError struct {
 	str string
 	err error
 }
 
-func NewFileAccessError(str string, err error) FileAccessError {
+func newFileAccessError(str string, err error) FileAccessError {
 	return FileAccessError{str: str, err: err}
 }
 
diff --git a/errors_test.go b/errors_test.go
index 0282def8..56e3421a 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -29,9 +29,10 @@ func TestTransferCloseStorageExceeded(t *testing.T) {
 }
 
 func TestErrorTypes(t *testing.T) {
-	a := assert.New(t)
+	// a := assert.New(t)
 	t.Run("DriverError", func(t *testing.T) {
-		var err error = NewDriverError("test", os.ErrPermission)
+		a := assert.New(t)
+		var err error = newDriverError("test", os.ErrPermission)
 		a.Equal("driver error: test: permission denied", err.Error())
 		a.ErrorIs(err, os.ErrPermission)
 
@@ -41,7 +42,8 @@ func TestErrorTypes(t *testing.T) {
 	})
 
 	t.Run("NetworkError", func(t *testing.T) {
-		var err error = NewNetworkError("test", os.ErrPermission)
+		a := assert.New(t)
+		var err error = newNetworkError("test", os.ErrPermission)
 		a.Equal("network error: test: permission denied", err.Error())
 		a.ErrorIs(err, os.ErrPermission)
 
@@ -51,7 +53,8 @@ func TestErrorTypes(t *testing.T) {
 	})
 
 	t.Run("FileAccessError", func(t *testing.T) {
-		var err error = NewFileAccessError("test", os.ErrPermission)
+		a := assert.New(t)
+		var err error = newFileAccessError("test", os.ErrPermission)
 		a.Equal("file access error: test: permission denied", err.Error())
 		a.ErrorIs(err, os.ErrPermission)
 		var specificError FileAccessError
diff --git a/handle_dirs.go b/handle_dirs.go
index 9b6ab7f3..cdd09d64 100644
--- a/handle_dirs.go
+++ b/handle_dirs.go
@@ -228,7 +228,7 @@ func (c *clientHandler) dirTransferNLST(w io.Writer, files []os.FileInfo, parent
 		_, err := w.Write([]byte(""))
 
 		if err != nil {
-			err = NewNetworkError("couldn't send NLST data", err)
+			err = newNetworkError("couldn't send NLST data", err)
 		}
 
 		return err
@@ -239,7 +239,7 @@ func (c *clientHandler) dirTransferNLST(w io.Writer, files []os.FileInfo, parent
 		// by a program to further process the files automatically.
 		// So we return paths relative to the current working directory
 		if _, err := fmt.Fprintf(w, "%s\r\n", path.Join(c.getRelativePath(parentDir), file.Name())); err != nil {
-			return NewNetworkError("couldn't send NLST data", err)
+			return newNetworkError("couldn't send NLST data", err)
 		}
 	}
 
@@ -304,7 +304,7 @@ func (c *clientHandler) dirTransferLIST(w io.Writer, files []os.FileInfo) error
 		_, err := w.Write([]byte(""))
 
 		if err != nil {
-			err = NewNetworkError("error writing LIST entry", err)
+			err = newNetworkError("error writing LIST entry", err)
 		}
 
 		return err
@@ -325,7 +325,7 @@ func (c *clientHandler) dirTransferMLSD(w io.Writer, files []os.FileInfo) error
 		_, err := w.Write([]byte(""))
 
 		if err != nil {
-			err = NewNetworkError("error writing MLSD entry", err)
+			err = newNetworkError("error writing MLSD entry", err)
 		}
 
 		return err
@@ -374,7 +374,7 @@ func (c *clientHandler) getFileList(param string, filePathAllowed bool) ([]os.Fi
 	// return list of single file if directoryPath points to file and filePathAllowed
 	info, err := c.driver.Stat(listPath)
 	if err != nil {
-		return nil, "", NewFileAccessError("couldn't stat", err)
+		return nil, "", newFileAccessError("couldn't stat", err)
 	}
 
 	if !info.IsDir() {
@@ -395,7 +395,7 @@ func (c *clientHandler) getFileList(param string, filePathAllowed bool) ([]os.Fi
 
 	directory, errOpenFile := c.driver.Open(listPath)
 	if errOpenFile != nil {
-		return nil, "", NewFileAccessError("couldn't open directory", errOpenFile)
+		return nil, "", newFileAccessError("couldn't open directory", errOpenFile)
 	}
 
 	defer c.closeDirectory(listPath, directory)
diff --git a/handle_files.go b/handle_files.go
index fa333ff1..bde6ff5f 100644
--- a/handle_files.go
+++ b/handle_files.go
@@ -165,7 +165,7 @@ func (c *clientHandler) doFileTransfer(tr net.Conn, file io.ReadWriter, write bo
 			fileTransferError.TransferError(err)
 		}
 
-		err = NewNetworkError("error transferring data", err)
+		err = newNetworkError("error transferring data", err)
 	}
 
 	return err
@@ -700,14 +700,14 @@ func (c *clientHandler) computeHashForFile(filePath string, algo HASHAlgo, start
 	if start > 0 {
 		_, err = file.Seek(start, io.SeekStart)
 		if err != nil {
-			return "", NewFileAccessError("couldn't seek file", err)
+			return "", newFileAccessError("couldn't seek file", err)
 		}
 	}
 
 	_, err = io.CopyN(h, file, end-start)
 
 	if err != nil && err != io.EOF {
-		return "", NewFileAccessError("couldn't read file", err)
+		return "", newFileAccessError("couldn't read file", err)
 	}
 
 	return hex.EncodeToString(h.Sum(nil)), nil
@@ -717,7 +717,7 @@ func (c *clientHandler) getFileHandle(name string, flags int, offset int64) (Fil
 	if fileTransfer, ok := c.driver.(ClientDriverExtentionFileTransfer); ok {
 		ft, err := fileTransfer.GetHandle(name, flags, offset)
 		if err != nil {
-			err = NewDriverError("calling GetHandle", err)
+			err = newDriverError("calling GetHandle", err)
 		}
 
 		return ft, err
@@ -726,7 +726,7 @@ func (c *clientHandler) getFileHandle(name string, flags int, offset int64) (Fil
 	ft, err := c.driver.OpenFile(name, flags, os.ModePerm)
 
 	if err != nil {
-		err = NewDriverError("calling OpenFile", err)
+		err = newDriverError("calling OpenFile", err)
 	}
 
 	return ft, err
diff --git a/server.go b/server.go
index 1e1a4546..0462b219 100644
--- a/server.go
+++ b/server.go
@@ -114,7 +114,7 @@ func (server *FtpServer) loadSettings() error {
 	s, err := server.driver.GetSettings()
 
 	if err != nil || s == nil {
-		return NewDriverError("couldn't load settings", err)
+		return newDriverError("couldn't load settings", err)
 	}
 
 	if s.PublicHost != "" {
@@ -172,7 +172,7 @@ func (server *FtpServer) Listen() error {
 		if err != nil {
 			server.Logger.Error("cannot listen on main port", "err", err, "listenAddr", server.settings.ListenAddr)
 
-			return NewNetworkError("cannot listen on main port", err)
+			return newNetworkError("cannot listen on main port", err)
 		}
 
 		if server.settings.TLSRequired == ImplicitEncryption {
@@ -183,7 +183,7 @@ func (server *FtpServer) Listen() error {
 			if err != nil || tlsConfig == nil {
 				server.Logger.Error("Cannot get tls config", "err", err)
 
-				return NewDriverError("cannot get tls config", err)
+				return newDriverError("cannot get tls config", err)
 			}
 
 			server.listener = tls.NewListener(server.listener, tlsConfig)
@@ -252,7 +252,7 @@ func (server *FtpServer) Serve() error {
 
 			server.Logger.Error("Listener accept error", "err", err)
 
-			return NewNetworkError("listener accept error", err)
+			return newNetworkError("listener accept error", err)
 		}
 
 		tempDelay = 0
@@ -301,7 +301,7 @@ func (server *FtpServer) Stop() error {
 			"err", err,
 		)
 
-		return NewNetworkError("couln't close listener", err)
+		return newNetworkError("couln't close listener", err)
 	}
 
 	return nil
diff --git a/server_test.go b/server_test.go
index 95b82631..a78027d9 100644
--- a/server_test.go
+++ b/server_test.go
@@ -89,7 +89,7 @@ func TestCannotListen(t *testing.T) {
 	portBlockerListener, err := net.Listen("tcp", "127.0.0.1:0")
 	a.NoError(err)
 
-	defer portBlockerListener.Close()
+	defer func() { a.NoError(portBlockerListener.Close()) }()
 
 	server := FtpServer{
 		Logger: lognoop.NewNoOpLogger(),
@@ -112,7 +112,7 @@ func TestListenWithBadTLSSettings(t *testing.T) {
 	portBlockerListener, err := net.Listen("tcp", "127.0.0.1:0")
 	a.NoError(err)
 
-	defer portBlockerListener.Close()
+	defer func() { a.NoError(portBlockerListener.Close()) }()
 
 	server := FtpServer{
 		Logger: lognoop.NewNoOpLogger(),
diff --git a/transfer_active.go b/transfer_active.go
index 82d904b8..7881b5a5 100644
--- a/transfer_active.go
+++ b/transfer_active.go
@@ -101,7 +101,7 @@ func (a *activeTransferHandler) Open() (net.Conn, error) {
 	conn, err := dialer.Dial("tcp", a.raddr.String())
 
 	if err != nil {
-		return nil, NewNetworkError("could not establish active connection", err)
+		return nil, newNetworkError("could not establish active connection", err)
 	}
 
 	if a.tlsConfig != nil {
@@ -118,7 +118,7 @@ func (a *activeTransferHandler) Open() (net.Conn, error) {
 func (a *activeTransferHandler) Close() error {
 	if a.conn != nil {
 		if err := a.conn.Close(); err != nil {
-			return NewNetworkError("could not close active connection", err)
+			return newNetworkError("could not close active connection", err)
 		}
 	}
 
@@ -161,7 +161,7 @@ func parsePORTAddr(param string) (*net.TCPAddr, error) {
 	addr, err := net.ResolveTCPAddr("tcp", fmt.Sprintf("%s:%d", ip, port))
 
 	if err != nil {
-		err = NewNetworkError(fmt.Sprintf("could not resolve %s", param), err)
+		err = newNetworkError(fmt.Sprintf("could not resolve %s", param), err)
 	}
 
 	return addr, err
@@ -203,7 +203,7 @@ func parseEPRTAddr(param string) (addr *net.TCPAddr, err error) {
 	addr, err = net.ResolveTCPAddr("tcp", net.JoinHostPort(ip.String(), strconv.Itoa(portI)))
 
 	if err != nil {
-		err = NewNetworkError(fmt.Sprintf("could not resolve addr %v:%v", ip, portI), err)
+		err = newNetworkError(fmt.Sprintf("could not resolve addr %v:%v", ip, portI), err)
 	}
 
 	return addr, err
diff --git a/transfer_pasv.go b/transfer_pasv.go
index 223c1fc4..01bf3848 100644
--- a/transfer_pasv.go
+++ b/transfer_pasv.go
@@ -47,11 +47,6 @@ func (e *ipValidationError) Error() string {
 	return e.error
 }
 
-const (
-	PortSearchMinAttempts = 10
-	PortSearchMaxAttempts = 1000
-)
-
 func (c *clientHandler) getCurrentIP() ([]string, error) {
 	// Provide our external IP address so the ftp client can connect back to us
 	ip := c.server.settings.PublicHost
@@ -84,14 +79,19 @@ func (c *clientHandler) getCurrentIP() ([]string, error) {
 // ErrNoAvailableListeningPort is returned when no port could be found to accept incoming connection
 var ErrNoAvailableListeningPort = errors.New("could not find any port to listen to")
 
+const (
+	portSearchMinAttempts = 10
+	portSearchMaxAttempts = 1000
+)
+
 func (c *clientHandler) findListenerWithinPortRange(portRange *PortRange) (*net.TCPListener, error) {
 	nbAttempts := portRange.End - portRange.Start
 
 	// Making sure we trying a reasonable amount of ports before giving up
-	if nbAttempts < PortSearchMinAttempts {
-		nbAttempts = PortSearchMinAttempts
-	} else if nbAttempts > PortSearchMaxAttempts {
-		nbAttempts = PortSearchMaxAttempts
+	if nbAttempts < portSearchMinAttempts {
+		nbAttempts = portSearchMinAttempts
+	} else if nbAttempts > portSearchMaxAttempts {
+		nbAttempts = portSearchMaxAttempts
 	}
 
 	for i := 0; i < nbAttempts; i++ {
@@ -102,7 +102,7 @@ func (c *clientHandler) findListenerWithinPortRange(portRange *PortRange) (*net.
 		if errResolve != nil {
 			c.logger.Error("Problem resolving local port", "err", errResolve, "port", port)
 
-			return nil, NewNetworkError(fmt.Sprintf("could not resolve port %d", port), errResolve)
+			return nil, newNetworkError(fmt.Sprintf("could not resolve port %d", port), errResolve)
 		}
 
 		tcpListener, errListen := net.ListenTCP("tcp", laddr)