Integration Testing C++ with Docker: A Practical Guide

Integration Testing C++ with Docker

Modern C++ development requires not only writing quality code, but also ensuring its reliable operation in real-world conditions. Integration testing is a key stage that allows you to check the interaction of system components: databases, network services, file systems. Using Docker for these purposes provides an isolated, reproducible environment that is ideal for CI/CD pipelines. In this article, we will look at how to set up integration testing of C++ applications using Docker, and provide practical examples.

Why Docker for C++ Integration Testing?

Traditional approaches to C++ integration testing often face problems:

• Environment dependency: tests may work on the developer's machine but fail on the build server due to different library versions.
• Setup complexity: testing with a real database or external API requires manual configuration.
• Parallel execution: multiple test runs can conflict due to shared resources.

Docker solves these problems by providing lightweight, isolated containers. You can spin up a test database, run your C++ service, and execute tests — all within a single docker-compose file. This guarantees that the environment will be identical on any machine.

Project Setup: Basic Example

Let's consider a simple C++ service that saves data to PostgreSQL. For integration testing we will need:

• The C++ code itself with tests (using Google Test).
• A Dockerfile for building and running tests.
• A docker-compose.yml for orchestrating containers.

Project structure:

my_cpp_project/├── src/│   ├── main.cpp│   ├── database.cpp│   └── database.h├── tests/│   └── test_integration.cpp├── CMakeLists.txt├── Dockerfile└── docker-compose.yml

Dockerfile:

FROM gcc:latest AS builder

WORKDIR /appCOPY . .

RUN apt-get update && apt-get install -y cmake libpq-devRUN cmake -B build -DCMAKE_BUILD_TYPE=ReleaseRUN cmake --build build

FROM ubuntu:22.04

RUN apt-get update && apt-get install -y libpq-devCOPY --from=builder /app/build/tests /app/testsCOPY --from=builder /app/build/my_app /app/my_app

ENTRYPOINT ["/app/tests"]

docker-compose.yml:

version: '3.8'services:  db:    image: postgres:15    environment:      POSTGRES_USER: testuser      POSTGRES_PASSWORD: testpass      POSTGRES_DB: testdb    ports:      - "5432:5432"    healthcheck:      test: ["CMD-SHELL", "pg_isready -U testuser -d testdb"]      interval: 5s      timeout: 5s      retries: 5

  test:    build: .    depends_on:      db:        condition: service_healthy    environment:      DB_HOST: db      DB_PORT: 5432      DB_USER: testuser      DB_PASSWORD: testpass      DB_NAME: testdb

Writing Integration Tests in C++

Now let's create a test that checks writing to and reading from the database. We'll use Google Test and the libpqxx library for working with PostgreSQL.

tests/test_integration.cpp:

#include <gtest/gtest.h>#include <pqxx/pqxx>#include <string>

class DatabaseTest : public ::testing::Test {protected:    void SetUp() override {        conn = new pqxx::connection(            "host=" + std::string(std::getenv("DB_HOST")) +            " port=" + std::string(std::getenv("DB_PORT")) +            " user=" + std::string(std::getenv("DB_USER")) +            " password=" + std::string(std::getenv("DB_PASSWORD")) +            " dbname=" + std::string(std::getenv("DB_NAME")));    }

    void TearDown() override {        delete conn;    }

    pqxx::connection* conn;};