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Write tests with Testcontainers

Table of contents

You have the CustomerService implementation ready, but for testing you need a PostgreSQL database. You can use Testcontainers to spin up a Postgres database in a Docker container and run your tests against it.

Add Testcontainers dependencies

Add the Testcontainers PostgreSQL module as a test dependency in pom.xml:

<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>testcontainers-postgresql</artifactId>
    <version>2.0.4</version>
    <scope>test</scope>
</dependency>

Since the application uses a Postgres database, the Testcontainers Postgres module provides a PostgreSQLContainer class for managing the container.

Write the test

Create CustomerServiceTest.java under src/test/java:

package com.testcontainers.demo;

import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.List;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.testcontainers.postgresql.PostgreSQLContainer;

class CustomerServiceTest {

  static PostgreSQLContainer postgres = new PostgreSQLContainer(
    "postgres:16-alpine"
  );

  CustomerService customerService;

  @BeforeAll
  static void beforeAll() {
    postgres.start();
  }

  @AfterAll
  static void afterAll() {
    postgres.stop();
  }

  @BeforeEach
  void setUp() {
    DBConnectionProvider connectionProvider = new DBConnectionProvider(
      postgres.getJdbcUrl(),
      postgres.getUsername(),
      postgres.getPassword()
    );
    customerService = new CustomerService(connectionProvider);
  }

  @Test
  void shouldGetCustomers() {
    customerService.createCustomer(new Customer(1L, "George"));
    customerService.createCustomer(new Customer(2L, "John"));

    List<Customer> customers = customerService.getAllCustomers();
    assertEquals(2, customers.size());
  }
}

Here's what the test does:

  • Declares a PostgreSQLContainer with the postgres:16-alpine Docker image.
  • The @BeforeAll callback starts the Postgres container before any test methods run.
  • The @BeforeEach callback creates a DBConnectionProvider using the JDBC connection parameters from the container, then creates a CustomerService. The CustomerService constructor creates the customers table if it doesn't exist.
  • shouldGetCustomers() inserts 2 customer records, fetches all customers, and asserts the count.
  • The @AfterAll callback stops the container after all test methods finish.
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