How to Resolve Illegal State Exception Errors When Running Tests with Embedded PostgreSQL

Why do my tests using embedded PostgreSQL fail with an Illegal State Exception?

// Example test setup for embedded PostgreSQL
import org.junit.jupiter.api.Test;
import org.testcontainers.containers.PostgreSQLContainer;

class EmbeddedPostgreSQLTest {
    private static final PostgreSQLContainer<?> postgres =
        new PostgreSQLContainer<>("postgres:latest").withDatabaseName("testdb").withUsername("user").withPassword("password");

    @Test
    void testDatabaseConnection() {
        postgres.start();
        // your database test logic here
        postgres.stop();
    }
}

When running tests that utilize an embedded PostgreSQL database, encountering an Illegal State Exception often indicates a configuration or lifecycle management issue. This error can arise from improper resource initialization and timing issues between test executions.

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

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

Causes

• The embedded PostgreSQL instance is not started before test execution begins.
• Database connection parameters are misconfigured or missing.
• Resource cleanup is not handled correctly, leading to stale connections during subsequent tests.
• PostgreSQL container fails to start due to resource constraints or incorrect Docker settings.

Solutions

• Ensure that the embedded database is properly initialized and started before tests are executed. Use lifecycle annotations like @BeforeAll to start the database.
• Verify your connection settings, including database URL, username, and password used in your tests.
• Incorporate proper resource management by cleaning up the database resources after each test to avoid conflicts using @AfterEach.
• Monitor your system resources and increase allocated memory or CPU for the embedded PostgreSQL container if necessary.

Mistake: Failing to start the PostgreSQL container before running tests.

Solution: Use the @BeforeAll annotation to ensure the container starts before any test methods are called.

Mistake: Not shutting down the PostgreSQL container after tests complete, leading to resource leaks.

Solution: Implement the @AfterAll annotation to cleanly stop the database container after all tests.

Mistake: Using hardcoded connection parameters that may not match the actual configuration.

Solution: Utilize environment variables or configuration files to manage your database settings dynamically.