C++ Unit Testing in C++


Unit testing is a level in software testing that validates the behavior and correctness of units of code.

In C++, "units of code" often refer to either classes, functions, or groups of either. Unit testing is often performed using specialized "testing frameworks" or "testing libraries" that often use non-trivial syntax or usage patterns.

This topic will review different strategies and unit testing libraries or frameworks.

Google Test

Google Test is a C++ testing framework maintained by Google. It requires building the gtest library and linking it to your testing framework when building a test case file.

Minimal Example

// main.cpp

#include <gtest/gtest.h>
#include <iostream>

// Google Test test cases are created using a C++ preprocessor macro
// Here, a "test suite" name and a specific "test name" are provided.
TEST(module_name, test_name) {
    std::cout << "Hello world!" << std::endl;
    // Google Test will also provide macros for assertions.
    ASSERT_EQ(1+1, 2);

// Google Test can be run manually from the main() function
// or, it can be linked to the gtest_main library for an already
// set-up main() function primed to accept Google Test test cases.
int main(int argc, char** argv) {
    ::testing::InitGoogleTest(&argc, argv);

    return RUN_ALL_TESTS();

// Build command: g++ main.cpp -lgtest


Catch is a header only library that allows you to use both TDD and BDD unit test style.

The following snippet is from the Catch documentation page at this link:

SCENARIO( "vectors can be sized and resized", "[vector]" ) {
    GIVEN( "A vector with some items" ) {
        std::vector v( 5 );
        REQUIRE( v.size() == 5 );
        REQUIRE( v.capacity() >= 5 );
        WHEN( "the size is increased" ) {
            v.resize( 10 );
            THEN( "the size and capacity change" ) {
                REQUIRE( v.size() == 10 );
                REQUIRE( v.capacity() >= 10 );
        WHEN( "the size is reduced" ) {
            v.resize( 0 );
            THEN( "the size changes but not capacity" ) {
                REQUIRE( v.size() == 0 );
                REQUIRE( v.capacity() >= 5 );
        WHEN( "more capacity is reserved" ) {
            v.reserve( 10 );
            THEN( "the capacity changes but not the size" ) {
                REQUIRE( v.size() == 5 );
                REQUIRE( v.capacity() >= 10 );
        WHEN( "less capacity is reserved" ) {
            v.reserve( 0 );
            THEN( "neither size nor capacity are changed" ) {
                REQUIRE( v.size() == 5 );
                REQUIRE( v.capacity() >= 5 );

Conveniently, these tests will be reported as follows when run:

Scenario: vectors can be sized and resized
     Given: A vector with some items
      When: more capacity is reserved
      Then: the capacity changes but not the size