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. (opens new window) 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

Catch (opens new window) is a header only library that allows you to use both TDD (opens new window) and BDD (opens new window) unit test style.

The following snippet is from the Catch documentation page at this link (opens new window):

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: