Undefined symbols for architecture x86_64: (linker issue?)

Question

I'm doing the following problem :

Add on to your Rectangle class from last time:

1)Create a new class TestRect which is a friend class of Rectangle. Inside this class, implement a member function called TestRect::tester, which takes a rectangle as a parameter and tests that both length and width are > 0.

2)Create a main() function which makes three rectangles r1, r2, and r3, each of which has length and width 20. Then call your TestRect::tester function on each of these rectangles and print out the result

I think I did part 1) correctly but part 2) does not give me the output I'm looking for. I do not know how to fix my code from the following output I got :

cppcompile rectEnhanceStaticFriends
Undefined symbols for architecture x86_64:
  "TestRect::tester(Rectangle&)", referenced from:
      _main in rectEnhanceStaticFriends.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
cppcompile:15: no such file or directory: ./rectEnhanceStaticFriends

Can you help me how to fix it? Seems a linker issue, that I did not find how to fix it. Thank you for reading through. (Ps: I compile with VSC) Here is my code :

rectEnhanceStaticFriends.cpp

#include <iomanip>
#include <cstring>
#include <string>
#include "rect.h"
using namespace std;

int main()
{

    Rectangle::setYards(100);
    Rectangle r1(20, 20, "Kitchen");
    Rectangle r2(20, 20, "Bathroom");
    Rectangle r3(20, 20, "Office");
    TestRect tr;

    cout << "Test on r1: " << tr.tester(r1) << endl;
    cout << "Test on r2: " << tr.tester(r2) << endl;
    cout << "Test on r3: " << tr.tester(r3) << endl;

    Rectangle house[] = {Rectangle(10, 12, "Kitchen"),
                         Rectangle(20, 20, "Bedroom"),
                         Rectangle(8, 12, "Offce")};

    for (int i = 0; i < 3; i++)
    {

        if (strcmp(house[i].printName(), "Offce") == 0)
        {
            // cout << "oui\n";
            house[i].setName("Office");
        };

        cout << "Area for " << house[i].printName() << " is : " << house[i].getArea() << endl;
    }

    if (house[1].getArea() > house[2].getArea() && house[1].getArea() > house[3].getArea())
    {
        cout << house[1].printName() << " has the biggest area.\n";
    }
    else if (house[2].getArea() > house[1].getArea() && house[2].getArea() > house[3].getArea())
    {
        cout << house[2].printName() << " has the biggest area\n";
    }
    else
    {
        cout << house[3].printName() << " has the biggest area\n";
    }

    //there is an error house[3] go beyond the array..
    return 0;
}

testRect.h

#ifndef TESTRECT_H
#define TESTRECT_H

class Rectangle; //forward declaration of class Rectangle

class TestRect
{
public:
    bool tester(Rectangle &);
};

#endif

testRect.cpp

#include <iostream> //
#include <iomanip>
#include <string>
#include "testRect.h"
#include "rect.h"

bool TestRect::tester(Rectangle &r)
{
    bool testResult = false;
    if (r.width > 0 && r.length > 0)
        testResult = true;
    return testResult;
}

rect.h

// Rec header file
#ifndef RECT_H
#define RECT_H
#include "testRect.h"

class Rectangle
{
private:
    double width;
    double length;
    char *name;
    static double yardsAvail; //indicate how many yards of perimeter are available to make rectangle
    void initName(const char *n);
    void initName(const char *n, int size);

public:
    //constructors
    Rectangle();
    Rectangle(double, double,
              const char *);
    //destructor
    ~Rectangle() { delete[] name; };
    void setWidth(double);
    void setLength(double);
    void setWidth(char *);
    void setLength(char *);
    void setName(const char *);
    int getWidth() const;
    int getLength() const;
    double getArea() const;
    char *printName() const
    {
        return name;
    }
    //added parts
    static void setYards(double);
    friend class TestRect;
    friend bool TestRect::tester(Rectangle &);
};
double Rectangle::yardsAvail = 0; //added parts

#endif

rect.cpp

#include <iostream> //
#include <iomanip>
#include <string>
#include "rect.h"
#include "testRect.h"
using namespace std;

Rectangle::Rectangle()
{
    width = 0;
    length = 0;
    initName("Default");
}

Rectangle::Rectangle(double x, double y, const char *z)
{
    width = x;
    length = y;
    initName(z);

    double yardsReqd = 2 * x + 2 * y;
    if (yardsAvail - yardsReqd < 0)
    {
        cout << "Not enough yard..\n";
        width = 0;
        length = 0;
    }

    yardsAvail -= yardsReqd;
}

void Rectangle::initName(const char *n)
{
    name = new char[258];
    strcpy(name, n);
};

void Rectangle::initName(const char *n, int size)
{
    name = new char[size];
    strcpy(name, n);
};

void Rectangle::setWidth(double w)
{
    width = w;
}

void Rectangle::setLength(double l)

{
    length = l;
}

void Rectangle::setName(const char *newname)
{
    //newname.newName = "Office";
    strcpy(name, newname);
}

double Rectangle::getArea() const
{
    return width * length;
}

//added part
void Rectangle::setYards(double y)
{
    yardsAvail = y;
}