Test containers for database testing in Spring Boot - Step-by-Step Execution

Concept Flow - Test containers for database testing

Start Test

↓

Initialize Test Container

↓

Start Database Container

↓

Run Application Tests

↓

Connect to Container DB

↓

Execute DB Operations

↓

Stop Container

↓

End Test

This flow shows how a test container starts a database, runs tests using it, then stops the container after tests finish.

Execution Sample

Spring Boot

import org.testcontainers.containers.PostgreSQLContainer;

static final PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15");

@PostConstruct
void startContainer() {
  postgres.start();
}

@Test
void testDbConnection() {
  // test logic here
  // e.g., use postgres.getJdbcUrl(), postgres.getUsername(), postgres.getPassword()
}

This code starts a PostgreSQL test container before tests and runs a test connecting to it.

Execution Table

Step	Action	Container State	DB Connection	Test Status
1	Initialize PostgreSQLContainer object	Not started	No connection	Not started
2	Call postgres.start()	Container starting	No connection	Not started
3	Container fully started	Running	Connection ready	Not started
4	Run test method	Running	Connected	Running
5	Execute DB queries	Running	Connected	Running
6	Test completes successfully	Running	Connected	Passed
7	Stop container	Stopped	No connection	Finished

💡 Test container stops after tests complete, releasing resources.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 6	Final
postgres	Created	Starting	Running	Running	Stopped
dbConnection	null	null	open	open	closed
testStatus	Not started	Not started	Not started	Passed	Finished

Key Moments - 3 Insights

Why do we need to start the container before running tests?

The container must be running to provide a real database for tests. See execution_table step 3 where the container is running and connection is ready.

What happens if the container is not stopped after tests?

Resources stay used and may cause conflicts or memory leaks. Step 7 shows stopping the container to clean up.

How does the test connect to the database inside the container?

The test uses connection info from the running container (step 4-5), ensuring tests run against a real isolated DB.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the database connection become ready?

A Step 2

B Step 4

C Step 3

D Step 7

💡 Hint

Check the 'DB Connection' column in execution_table rows.

According to variable_tracker, what is the state of 'postgres' after step 6?

A Created

B Running

C Starting

D Stopped

💡 Hint

Look at the 'postgres' row and the 'After Step 6' column.

If the container is not stopped, what would be the final value of 'testStatus' in variable_tracker?

A Passed

B Running

C Not started

D Finished

💡 Hint

Stopping container changes 'testStatus' to 'Finished' as per variable_tracker final column.

Concept Snapshot

Test containers start a real database in a container before tests run.
Tests connect to this isolated DB for realistic testing.
After tests, the container stops to free resources.
Use @PostConstruct or setup methods to start containers.
Use container-provided connection info in tests.
Always stop containers to avoid resource leaks.

Full Transcript

Test containers for database testing work by starting a real database inside a container before tests run. The test code connects to this database using connection details provided by the container. Tests execute queries against this isolated database, ensuring realistic and clean test environments. After tests finish, the container is stopped to release resources and avoid conflicts. This process involves initializing the container object, starting it, running tests connected to it, and stopping it after tests complete. Variables like the container state, database connection, and test status change step-by-step during this flow.