Running a Serial loop via a funciton call

Hello!
I am trying to make a simple data receiver but i am stuck here any help is appreciated.

void setup() {
  Serial.begin(9600);
}

void loop() {
  in_Parser();
}

void in_Parser(){
  static byte in_packet = byte(252);
  
    if (Serial.available() > 0){
      
      byte _in = Serial.read();
		if (_in == in_packet){
			Serial_test();
			return;
		   }
  }
}

void Serial_test(){
  Serial.println("Here");
  while (Serial.available() > 0){
    byte in = Serial.read();
    Serial.println(in);
  }

}

What i cannot understand is that why doesn't the while loop in the Serial_test function take over in reading the serial buffer.

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data. There is also a parse example to illustrate how to extract numbers from the received text.

...R