This tutorial focuses on creating a simple C++ Calculator project using the divide() function and testing it using the GoogleTest platform. This guide shows a complete way to do this, starting by writing tests for that function and then moving on to writing the source for the function. The principle of Test Driven Development (TDD) is to write the tests first, and then the function itself. As you write your source code, you should run tests from time to time to check that the code is correct.

...

...

Create The Calculator project

...

To present an example of using GoogleTest, we first need to create a project in C++.  In the project directory named Calculator, before starting to write codes, it is necessary to prepare its structure. It will need two subdirectories named src and tst - one for the source codes and one for the tests codes. At this point, these folders can be filled with empty files with appropriate names for sources: operation.cpp; operations.h, and for tests: run_tests.cpp; test_operations.cpp. However, each of these files can be created later during development.

 Tests

 Tests supervisor file

To start writing tests, it is needed to create run_tests.cpp and test_operations.cpp (if not done previously). In order to force GoogleTest to automatically search for test files, the file run_tests.cpp comes in handy. Typically, a code inside this file will be universal for all kinds of projects:

#include "gtest/gtest.h"

int main(int argc, char **argv){
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

 Tests suites file

However, the actual test cases are placed in a separate file, the name of which corresponds to the name of the file that stores the code to be tested. It is good practice to name the test file using the name of the source file being tested with the keyword test appended as a prefix or suffix separated by the underscore "_" or the dash "-". The goal of this tutorial is to test the division function stored in operations.cpp, although it does not exist at this point, it is predicted that it will be. Therefore, the file with the test code is named test_operations.cpp, and should look like this:

#include <gtest/gtest.h>
#include "operations.h"

TEST(DivideOperation, PositiveInput) {
    // Integer arguments
    ASSERT_EQ(divide(10, 5), 2);
    ASSERT_FLOAT_EQ(divide(5, 10), 0.5);
    // Floating-point arguments
    ASSERT_FLOAT_EQ(divide(10.0f, 5.0f), 2.0f);
    ASSERT_FLOAT_EQ(divide(5.0f, 10.0f), 0.5f);
}

TEST(DivideOperation, NegitiveInput) {
    // Integer arguments
    ASSERT_EQ(divide(-10, -5), 2);
    ASSERT_FLOAT_EQ(divide(-5, -10), 0.5);
    // Floating-point arguments
    ASSERT_FLOAT_EQ(divide(-10.0f, -5.0f), 2.0f);
    ASSERT_FLOAT_EQ(divide(-5.0f, -10.0f), 0.5f);
}

TEST(DivideOperation, ZerioInput) {
    // Integer arguments
    EXPECT_THROW(divide(10, 0), std::overflow_error);
    // Floating-point arguments
    EXPECT_THROW(divide(10.0f, 0.0f), std::overflow_error);
}

...