Google Test: error LNK2019: unresolved external symbol with Visual Studio 2013

Question

I'm trying to get my first ever unit test with Google Test framework + Visual Studio 2013.However I'm hitting the below error and can't understand why.

1>------ Build started: Project: FirstGoogleTest, Configuration: Debug Win32 ------
2>------ Build started: Project: googleTest, Configuration: Debug Win32 ------
1> MyMultiplier.cpp
2> gtest_main.cc
1> main.cpp
1> Generating Code...
2> gtest-all.cc
1> FirstGoogleTest.vcxproj -> D:_Vault\Workspaces\UnitTestLearning\FirstGoogleTest\Debug\FirstGoogleTest.exe
2> Generating Code...
2> googleTest.vcxproj -> D:_Vault\Workspaces\UnitTestLearning\FirstGoogleTest\Debug\googleTest.lib
3>------ Build started: Project: MyMultiplier_UnitLevelTest, Configuration: Debug Win32 ------
3> MyMultiplier_UnitLevelTest.cpp
3>MyMultiplier_UnitLevelTest.obj : error LNK2019: unresolved external symbol "public: unsigned int __thiscall
MyMultiplier::multiply(unsigned int,unsigned int)" (?multiply@MyMultiplier@@QAEIII@Z) referenced in function "private: virtual void __thiscall MyMultiplier_multiplyNormalSmallValues_Test::TestBody(void)" (?TestBody@MyMultiplier_multiplyNormalSmallValues_Test@@EAEXXZ)
3>D:_Vault\Workspaces\UnitTestLearning\FirstGoogleTest\Debug\MyMultiplier_UnitLevelTest.exe : fatal error LNK1120: 1 unresolved externals
========== Build: 2 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

The solution structures is as follow:
https://www.dropbox.com/s/0cu8eqr7pz3ajaz/Untitled.png

The ULT project's "References" projects include "googleTest" and "FirstGoogleTest". here is the "MyMultiplier_UnitLevelTest.cpp"

#include "gtest/gtest.h"  // access test macro
#include "MyMultiplier.h"   // testee
#include <iostream>
#include <string>

TEST(MyMultiplier, multiplyNormalSmallValues){
    MyMultiplier m;
    std::string name("MyMultiplier_ULT");
    unsigned int a = 5;
    unsigned int b = 10;
    unsigned int answer = m.multiply(a, b/*, name*/);
    ASSERT_EQ(a * b, answer);

}

the "multiply" function's declaration in MyMultiplier.h:

class MyMultiplier{
public:
    unsigned int multiply(unsigned int a, unsigned int b/*, std::string& name*/);
};

the signature matches and also the header file is included. why the ult project can't find the symbol?

the entire solution can be downloaded here: https://www.dropbox.com/sh/vc89o5ep139wkuk/AAA8Z76q6iAkP25zTmu9bR3ia

Answer 1

I solved a similar problem by including the cpp files (I created a Visual Studio Project for testing with GoogleTest my own class "Number" (.h + .cpp))

Didn't work:

#include "pch.h"
#include "..\..\LAB2\Number.h"

class TestLab2 : public ::testing::Test {
public:
    TestLab2() {
        Number n;
    }
}

Worked:

#include "pch.h"
#include "..\..\LAB2\Number.h"
#include "..\..\LAB2\Number.cpp"

class TestLab2 : public ::testing::Test {
public:
    TestLab2() {
        Number n;
    }
}

Answer 2

The root cause is the project type is not set correctly.

In this example, there are three projects:

1. FirstGoogleTest, which is the testee. the class to be tested resides in here.
   
2. googleTest, which is the google test framework
   
3. MyMultiplier_UnitLevelTest, which is the ULT project that contains the tests.
   

The root cause is "FirstGoogleTest" project's configuration Type was set to .exe, which is the same as the ULT project. so the ult test cannot get the externals from "FirstGoogleTest". After changing "FirstGoogleTest" configuration Type to Static library (.lib). the solution can be compiled correctly and the ULT runs fine.