Google Test Returning Garbage Values For Working Operations

Question

I have tested the .decreaseInventory() manually in my main file so I know it works correctly but when I run a google test on it, it fails and gives me an error. How could I fix this?

Player class:

#ifndef PLAYER_H
#define PLAYER_H

#include <iostream>  
using namespace std;

class Player
{

    int inventory;

public:
    Player();
    int decreaseInventory(int numOfBeers);
    void setInventory(int newInventory);
    int getBackOrder();
    int getCost();
    int getInventory();

    bool operator ==(Player& p);
};

Player::Player()
{
    cout << " Default Player Constructor\n";
    inventory = 12;
    backorder = 0;
    cost = 0;
    orderDelay = 0;
    shipmentDeplay = 0;
}

void Player::setInventory(int newInventory)
{
    inventory = newInventory;
}

int Player::decreaseInventory(int numOfBeers)
{
    inventory = inventory - numOfBeers;
}

int Player::getInventory()
{
    return inventory;
}

test.cpp:

#include "gtest/gtest.h"
#include "Player.h"

TEST(playerTest, decreaseInventoryTest ) {

    Player p;
    int curr_inv = p.getInventory();
    EXPECT_EQ(curr_inv-3, p.decreaseInventory(3));

}

Error:

Running main() from gtest_main.cc
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from playerTest
[ RUN      ] playerTest.decreaseInventoryTest
 Default Player Constructor
/home/hammad/se-02-team-21/tests.cpp:13: Failure
      Expected: curr_inv-3
      Which is: 9
To be equal to: p.decreaseInventory(3)
      Which is: 1740894128
[  FAILED  ] playerTest.decreaseInventoryTest (1 ms)
[----------] 1 test from playerTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] playerTest.decreaseInventoryTest

 1 FAILED TEST

Why does it fail and give a garbage value? I am already using a default constructor and in general it works properly.

Answer 1

Your method is:

int Player::decreaseInventory(int numOfBeers)
{
    inventory = inventory - numOfBeers;
}

Your test is:

EXPECT_EQ(curr_inv-3, p.decreaseInventory(3));

The macro EXPECT_EQ compares the value returned from p.decreaseInventory(3) with curr_inv-3. The method does not return anything.

Not returning something from a method that is declared to return something is undefined behavior. Your compiler should have warned you about it and your test was successful in the sense that you have a failing test that is caused by a real bug in your code that you now can fix.