docker-docs/content/guides/testcontainers-java-getting-started/write-tests.md

title, linkTitle, description, weight

title	linkTitle	description	weight
Write tests with Testcontainers	Write tests	Write your first integration test using Testcontainers for Java and PostgreSQL.	20

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.