Problem in writing "DivideByZero" Unit test case using CPPUnitTest in Visual Studio 2019 C++

Question

Unit testing means writing code that verifies individual parts, or units, of an application or library. A unit is the smallest testable part of an application. Unit tests assess code in isolation. In C++ this means writing tests for methods or functions. I am writing a basic calculator program and trying to use CPPUnitTest to test the code in Visual studio 2019.After that I have to build this in Jenkins too. Please don't judge .. I am writing unit Test for the 1st time .. this is my Calculator.cpp

#include <iostream>
#include "Calc.h"
using namespace std;

int main()
{
        Calc obj;
        float a, b;
        cin >> a >> b;
        int menu;
        cout << "Enter what operation you want(1-4);" << endl;
        cout << "1. Addition" << endl;
        cout << "2. Subtraction" << endl;
        cout << "3. Multiplication" << endl;
        cout << "4. Division" << endl;
        cin >> menu;
        switch (menu)
        {
        case 1:obj.add(a, b);
            break;
        case 2:obj.sub(a, b);
            break;
        case 3:obj.multiply(a, b);
            break;
        case 4:
            try
            {
                obj.divide(a, b);
            }
            catch (std::runtime_error& e)
            {
                cout << e.what() << "\n";
            }
            break;
        default:
        {
            cout << "Invalid input" << endl;
        }
    }
}

This is class Calc or "Calc.h" Here I have used std::runtime_error to throw error on division bye zero

#pragma once
#include <stdexcept>
class Calc {

public:
    float add(float a, float b)
    {
        return a + b;
    }
    float sub(float a, float b) {

        return  a - b;
    }

    float multiply(float a, float b) {
        return  a * b;
    }

    float divide(float a, float b) {
        if (b == 0)
        {
            throw std::runtime_error("Division by zero condition!");
        }
        return a / b;
    }

};

I am trying to write unit test using CPPUnitTest for my code. I have written code for add and subtract using assert::AreEqual but for divide by zero condition, I don't know to write the test case. this is my unit test code.

#include "pch.h"
#include "CppUnitTest.h"
#include "../Calculator/Calc.h"
#include <stdexcept>

using namespace std;
using namespace Microsoft::VisualStudio::CppUnitTestFramework;

namespace CalculatorTest
{
    TEST_CLASS(CalculatorTest)
    {
    public:
        Calc cal;
        TEST_METHOD(AddTest)
        {
            float k = cal.add(3, 4);
            Assert::AreEqual(7.0f,k);
        }
        TEST_METHOD(SubTest)
        {
            float k = cal.sub(3, 4);
            Assert::AreNotEqual(-2.0f, k);
        }
        TEST_METHOD(DivByZeroTest)
        {
            //what should I write here
        }
    };
}

Please help me to write the test method for this . Somewhere I read CPPUNIT_ASSERT_THROW(cal->divide(12,0), std::runtime_error); but this is not working in my case. How can I make Assert::AreEqual Also suggest which else method I can use to increase my code coverage.

Answer 1

You should not use assert::AreEqual when checking for exceptions. You could wrap your exception throwing code in a lambda and pass it to Assert::ExpectException<std::runtime_error>, which should assert true if the expected exception is thrown:

    TEST_METHOD(DivByZeroTest)
    {
        auto func = [] { return cal.divide(1.f, 0.f); };
        Assert::ExpectException<std::runtime_error>(func);
    }

I expect that this does something like this internally::

bool result = false;
try {
    func();
} catch(const std::runtime_error&) {
    result = true;
} catch(...) {
}
return result;