Replace @ClassRule with `static {}` block

[bsideup]

Hi!

@ClassRule here will restart the container in each test class:

event-sourcing-microservices-example/user-service/src/test/java/io/example/AbstractUnitTest.java

Lines 27 to 28 in 28438ee

	public static GenericContainer postgres = new GenericContainer("postgres:9.6.8")
	.withExposedPorts(5432)

While Spring Boot reuses the context between tests. As soon as you add one more integration test class, your tests will start failing.

It is recommended to use a "Singleton container" pattern here and replace this code:

@ClassRule
public static GenericContainer postgres = new GenericContainer("postgres:9.6.8")
			.withExposedPorts(5432)
			.withEnv("POSTGRES_PASSWORD", "password")
			.withEnv("POSTGRES_USER", "postgres");

with this:

public static GenericContainer postgres = new GenericContainer("postgres:9.6.8")
			.withExposedPorts(5432)
			.withEnv("POSTGRES_PASSWORD", "password")
			.withEnv("POSTGRES_USER", "postgres");

static {
    postgres.start();
}

Or maybe even consider using the JDBC URL support:
https://www.testcontainers.org/usage/database_containers.html#jdbc-url
https://testcontainers.gitbook.io/workshop/step-4-your-first-testcontainers-integration