Error Help Request : "undefined reference to..."

[Volk2013]

I'm working on unit testing an assignment of mine, and i'm at a loss. Can someone help me understand what is going on here?

Below, in order is (1) the output from make (2) the tester file, test.cc (3) the header file for the .cc being test, called msg.h (4) makefile

Thanks for your time

//**OUTPUT*FROM*MAKE*********************************************************
g++   -std=c++11   -Wall       -c   msg.cc 
g++   -std=c++11   -Wall       -c   test.cc
g++   -std=c++11   -Wall       -o   test msg.o test.o

test.o: In function `main':
test.cc:(.text+0x6b): undefined reference to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

test.cc:(.text+0xd2): undefined reference to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

test.cc:(.text+0x139): undefined reference to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

test.cc:(.text+0x1a0): undefined reference to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

test.cc:(.text+0x207): undefined reference to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

test.o:test.cc:(.text+0x26f): more undefined references to `Message::Validate(std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> > const&)' follow

collect2: error: ld returned 1 exit status
makefile:11: recipe for target 'test' failed
make: *** [test] Error 1

//**Test.cc*********************************************************

#include "msg.h"

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

#include <string>
using std::string;
using std::to_string;

#include <cstdlib>
using std::rand;
using std::srand;

#include <ctime>
using std::time;

string Create_Correct_Ones();
string Create_Correct_Tens();
string Create_Correct_Hundreds();
string Create_Correct_Thousands();
string Create_No_M();
string Create_No_Percent_One();
string Create_No_Percent_Two();
string Create_Non_Int();
string Create_End_Early();
int Test_GetBodyLength();
int Test_GetBody();

int main(int argc, char* argv[]) {
  cout << "" << endl;
  cout << "TESTING VALIDATE:" << endl;

  if(Message :: Validate(Create_Correct_Ones()) != 0)
    cout << "TEST Create_Correct_Ones() Failed    EXPECTED: PASSED" << endl;
  else
    cout << "TEST Create_Correct_Ones() Passed    EXPECTED: PASSED" << endl;
  
  //Format above repeated for all tests

  return 0;
}

//**************************************************************

// Returns a string with correct message formating for a message with a 
// length that is less than ten characters in length

string Create_Correct_Ones(){
  //Left Empty  
} 

//**************************************************************

// Returns a string with correct message formating for a message with a 
// length that is less than one-hundred characters in length

string Create_Correct_Tens(){
  //Left Empty
} 

//**************************************************************

// Returns a string with correct message formating for a message with a 
// length that is less than one-hundred characters in length

string Create_Correct_Hundreds(){
  //Left Empty
} 

//**************************************************************

// Returns a string with correct message formating for a message with a 
// length that is less than one-thousand characters in length

string Create_Correct_Thousands(){
  //Left Empty
} 

//**************************************************************

// Returns a string with a message that is missing the m formating

string Create_No_M(){
  //Left Empty
}

//**************************************************************

// Returns a string with a message that is missing the first %

string Create_No_Percent_One(){
  //Left Empty
}

//**************************************************************

// Returns a string with a message that is missing the second %
string Create_No_Percent_Two(){
  //Left Empty
}

//**************************************************************

// Returns a string with a message that has a non-int in formating
string Create_Non_Int(){
  //Left Empty
}

//**************************************************************

// Returns a string with a message that ends early
string Create_End_Early(){
  //Left Empty
}

//**************************************************************

// Tests function of GetBody() 
int Test_GetBody(){
  //Left Empty
}

//**msg.h********************************************************

//#ifndef _HW3_INCLUDE_MSG_H_ // NOLINT
//#define _HW3_INCLUDE_MSG_H_ // NOLINT

#include <iostream>
using std::cout;
using std::cin;
using std::endl;
#include <string>
using std::string;
using std::to_string;

class Message {
 public:

 // static methods
  /*  Validates a message string e.g. m%6%my msg  */
  static int Validate(const std::string& msg);
  /*  Creates a from a message string e.g. m%6%my msg  */
  static const Message MsgFromMsgStr(const std::string& msg);

//**************************************************************
 // constructors
  /* Sets Message instance's body to empty string  */
  Message(); // NOLINT
  /*  Sets Message instance's body to char array parameter  */
  Message(const char body[]); // NOLINT
  /*  Sets Message instance's body to string parameter.  */
  Message(const std::string& body); // NOLINT

//**************************************************************

 // accessors
  const std::string GetBody() const;
  /*
   *  Returns the length of the Message instance's body.
   */
  unsigned int GetLength() const;

  /*
   *  Returns a string message of the form m%<body length>%<body>
   */
  const std::string ToString() const;

//**************************************************************

 // mutators
  /*
   *  Method accepts a string and appends it to the Message instance's body.
   */
  void AppendToBody(const std::string& body);

//**************************************************************

 // comparators
  /*
   *  Returns true if two messages have the same body.
   */
  bool Equals(const Message& that) const;

//**************************************************************

 // operators
  /*
   *  Operator accepts a string which is appended to the Message's body
   *  and returned as a new Message.
   */
  const Message operator+(const std::string& body) const;

  /*
   *  Returns true if two messages have the same body.
   */
  bool operator==(const Message& that) const;
 
//**************************************************************

 private:
  string msg_;
  int length_;
};

//**MAKEFILE****************************************************

CC = g++  # use g++ compiler

FLAGS = -std=c++11  # compile with C++ 11 standard
FLAGS += -Wall      # compile with all warnings

LINK = $(CC) $(FLAGS) -o  # final linked build to binary executable

COMPILE = $(CC) $(FLAGS) -c  # compilation to intermediary .o files

test : msg.o test.o
	$(LINK) $@ $^

test.o : test.cc msg.h
	$(COMPILE) $<

msg.o : msg.cc msg.h
	$(COMPILE) $< 

clean:
	@rm test *.o

//************************************************************** 

[tpb]

Presumably there's something wrong with your definition of

  static int Validate(const std::string& msg);

in msg.cc. But you didn't show that file.