Test containers for database testing in JUnit - Test Execution Trace

Test Overview

This test uses Testcontainers to start a temporary PostgreSQL database. It verifies that the application can connect and query the database correctly.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.api.Test;
import org.testcontainers.containers.PostgreSQLContainer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class PostgresContainerTest {

    @Test
    public void testDatabaseConnection() throws Exception {
        try (PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15.3")) {
            postgres.start();

            String jdbcUrl = postgres.getJdbcUrl();
            String username = postgres.getUsername();
            String password = postgres.getPassword();

            try (Connection conn = DriverManager.getConnection(jdbcUrl, username, password);
                 Statement stmt = conn.createStatement()) {

                stmt.execute("CREATE TABLE test_table(id INT PRIMARY KEY, name VARCHAR(255));");
                stmt.execute("INSERT INTO test_table VALUES (1, 'Test User');");

                ResultSet rs = stmt.executeQuery("SELECT name FROM test_table WHERE id = 1;");

                if (rs.next()) {
                    String name = rs.getString("name");
                    assertEquals("Test User", name);
                } else {
                    throw new AssertionError("No data found in test_table");
                }
            }
        }
    }
}

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initializes the test method	-	PASS
2	PostgreSQLContainer is created and started	A Docker container with PostgreSQL 15.3 is running and ready to accept connections	Container started successfully	PASS
3	Connect to the PostgreSQL database using JDBC URL, username, and password from container	Connection to the temporary database is established	Connection is not null and valid	PASS
4	Execute SQL to create table 'test_table'	Table 'test_table' created in the database	Table creation executed without error	PASS
5	Insert a row into 'test_table' with id=1 and name='Test User'	One row inserted into 'test_table'	Insert executed without error	PASS
6	Query 'test_table' for name where id=1	ResultSet contains one row with name='Test User'	ResultSet has next row	PASS
7	Assert that the retrieved name equals 'Test User'	Assertion compares expected and actual values	assertEquals("Test User", name)	PASS
8	Stop the PostgreSQL container and end the test	Docker container is stopped and removed	-	PASS

Failure Scenario

Failing Condition: The test fails if the container does not start or the database connection cannot be established.

Execution Trace Quiz - 3 Questions

What does the test verify after inserting data into the database?

A That the table 'test_table' exists

B That the database container is running

C That the inserted name matches 'Test User'

D That the connection URL is correct

Key Result

Using Testcontainers allows tests to run against a real database in a clean environment, improving reliability and avoiding dependencies on external databases.