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Unit Testing

Introduction to Unit Testing in C++

Unit testing is a method used to verify the correctness of a unit of source code. Such a unit could be a function, a class, a method, or any other small, testable part of the software. The goal of unit testing is to ensure that each individual part of the program works correctly and as expected.

Importance of Unit Testing​

Besides verifying that your code behaves as expected, unit testing has several other benefits:

  1. Helps Find and Fix Bugs Early: Bugs detected early in the software lifecycle are less expensive to fix.
  2. Simplifies Code: Writing tests for functions or methods often leads to more modular, flexible, and extensible code.
  3. Documents the Code: Unit tests can serve as a form of documentation by demonstrating how a piece of code should behave.

Writing a Simple Unit Test​

Let's start with a simple function, which we will later test.

int add(int a, int b) {
    return a + b;
}

This function takes two integers as arguments and returns their sum. Now, let's write a unit test for this function.

void testAdd() {
    assert(add(1, 2) == 3);
    assert(add(-1, -2) == -3);
    assert(add(0, 0) == 0);
    cout << "All test cases passed for add() function\n";
}

In the above test function, we use the assert function to test the add function. If the condition within the assert statement is true, the program continues. If it's false, the program displays an error message and terminates.

C++ Testing Frameworks​

While it's possible to write unit tests as shown above, it's often more convenient and effective to use a testing framework. There are several unit testing frameworks available for C++, such as:

  • Google Test: Google's framework for writing C++ tests on a variety of platforms.
  • Boost.Test: Part of the Boost library, a set of peer-reviewed, portable C++ source libraries.
  • Catch2: A modern, C++-native, test framework for unit-tests, TDD and BDD.

Example with Google Test​

Here's how we could write our earlier test using Google Test:

#include <gtest/gtest.h>

TEST(AddTest, PositiveNumbers) {
    EXPECT_EQ(add(1, 2), 3);
}

TEST(AddTest, NegativeNumbers) {
    EXPECT_EQ(add(-1, -2), -3);
}

TEST(AddTest, Zeroes) {
    EXPECT_EQ(add(0, 0), 0);
}

Google Test uses macros to define tests. TEST macro takes two parameters: the test case name and the test name. The EXPECT_EQ macro is similar to the assert function we used earlier.

Conclusion​

Unit testing is a critical part of software development. It helps ensure that your code is reliable and working as expected. The examples above illustrate how to write a simple unit test in C++. However, to fully leverage the power of unit testing, you should consider using a testing framework such as Google Test, Boost.Test, or Catch2.

Remember, the key to successful unit testing is to write tests for every function or method in your code. Happy testing!