SpringBootTest does not roll back - spring-boot

Question

(Although, there are plenty of similar questions I was not able to find the solution among them).
Why #Transactional annotation with #SpringBootTest works and rolls back nicely when I use DAO directly, but does not work when I test with TestRestTemplate?
tl;dr
Entity
#Entity
public class ToDoItem {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#NotNull #Column(unique = true)
private String title;
public ToDoItem() {}
public ToDoItem(String title) { this.title = title;}
// getters, setters, etc.
Repository
public interface ToDoRepository extends CrudRepository<ToDoItem, Long> {}
Application
#EnableTransactionManagement
#SpringBootApplication
#RestController
#RequestMapping("/todos")
public class ToDoApp {
public static void main(String[] args) {
SpringApplication.run(ToDoApp.class, args);
}
#Autowired
private ToDoRepository toDoRepository;
#GetMapping
ResponseEntity<?> fetchAll() { return ok(toDoRepository.findAll()); }
#PostMapping()
ResponseEntity<?> createNew(#RequestBody ToDoItem toDoItem) {
try {
toDoRepository.save(toDoItem);
return noContent().build();
} catch (Exception e) {
return badRequest().body(e.getMessage());
}
}
}
Now I create two tests which do basically the same: store some to-do items in in-memory database and check if size has increased:
Repository test
#ExtendWith(SpringExtension.class)
#SpringBootTest
#Transactional
class ToDoRepoTests {
#Autowired
private ToDoRepository toDoRepository;
#Test
void when_adding_one_item_then_success() {
toDoRepository.save(new ToDoItem("Run tests"));
assertThat(toDoRepository.findAll()).hasSize(1);
}
#Test
void when_adding_two_items_then_success() {
toDoRepository.saveAll(List.of(
new ToDoItem("Run tests"), new ToDoItem("Deploy to prod")));
assertThat(toDoRepository.findAll()).hasSize(2);
}
}
Then I create similar test that does exactly the same thing but via REST API (This one does not work and fails with Unique index or primary key violation):
#ExtendWith(SpringExtension.class)
#SpringBootTest(classes = ToDoApp.class, webEnvironment = WebEnvironment.RANDOM_PORT)
#Transactional
class ToDoControllerTests {
#LocalServerPort
private int localServerPort;
private TestRestTemplate testRestTemplate;
#BeforeEach
void setUp() {
testRestTemplate = new TestRestTemplate(new RestTemplateBuilder()
.rootUri("http://localhost:" + localServerPort));
}
#Test
void when_adding_one_item_then_success() {
// when
createToDo(new ToDoItem("Walk the dog"));
var allItems = fetchAllTodos();
// then
assertThat(allItems).hasSize(1);
}
#Test
void when_adding_two_items_then_success() {
// when
createToDo(new ToDoItem("Walk the dog"));
createToDo(new ToDoItem("Clean the kitchen"));
var allItems = fetchAllTodos();
// then
assertThat(allItems).hasSize(2);
}
private void createToDo(ToDoItem entity) {
var headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
var response = testRestTemplate.postForEntity("/todos", new HttpEntity<>(entity, headers), String.class);
assertThat(response.getStatusCode()).isEqualTo(NO_CONTENT);
}
private List<ToDoItem> fetchAllTodos() {
return Arrays.asList(testRestTemplate.getForObject("/todos", ToDoItem[].class));
}
}
And here is my pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.5.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>foo.bar</groupId>
<artifactId>todo-app</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>To-Do App</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<version>5.4.2</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>11</source>
<target>11</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
Please, help me to understand, what I am doing wrong.

Answer 1

When you call the API using the RESTTemplate it crosses the boundary of the local transaction management and becomes as distributed transaction. There is not mechanism available for spring to roll back that call to the rest API. Although in your example the target system is the same application, it need not be so. It could be an external application that is not aware of the transactional boundaries that you have set in your test.