TestRestTemplate for full integration in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this TestRestTemplate GET request?

Given a Spring Boot REST controller that returns a JSON object {"message": "Hello World"} at endpoint /greet, what will this TestRestTemplate call return?

Spring Boot

ResponseEntity<String> response = testRestTemplate.getForEntity("/greet", String.class);
String body = response.getBody();
System.out.println(body);

A {"msg":"Hello World"}

B {"message":"Hello World"}

C null

D Hello World

💡 Hint

Remember the controller returns a JSON object with key 'message'.

The controller returns a JSON object with key 'message' and value 'Hello World'. The TestRestTemplate getForEntity returns the raw JSON string in the body.

❓ state_output

intermediate

What is the HTTP status code after a successful POST with TestRestTemplate?

A Spring Boot controller accepts POST requests at /items and returns ResponseEntity with status CREATED (201). What status code will testRestTemplate.postForEntity("/items", newItem, Item.class).getStatusCodeValue() return?

Spring Boot

ResponseEntity<Item> response = testRestTemplate.postForEntity("/items", newItem, Item.class);
int statusCode = response.getStatusCodeValue();
System.out.println(statusCode);

A 201

B 404

C 200

D 500

💡 Hint

Check the controller's ResponseEntity status for POST.

The controller returns ResponseEntity with status CREATED (201), so the TestRestTemplate response status code is 201.

📝 Syntax

advanced

Which TestRestTemplate call correctly sends a PUT request with a JSON body?

You want to update an item at /items/5 using TestRestTemplate. Which option correctly sends a PUT request with the updated item object?

A testRestTemplate.exchange("/items/5", HttpMethod.PUT, new HttpEntity<>(updatedItem), Item.class);

B testRestTemplate.put("/items/5", updatedItem, Item.class);

C testRestTemplate.put("/items/5", updatedItem);

D testRestTemplate.postForEntity("/items/5", updatedItem, Item.class);

💡 Hint

PUT requests with body often use exchange method with HttpEntity.

Option A uses exchange with HttpMethod.PUT and HttpEntity wrapping the updatedItem, which is the correct way to send a PUT with body. Option A is valid but does not return a response. Option A is invalid because put method does not take a response type. Option A uses POST instead of PUT.

🔧 Debug

advanced

Why does this TestRestTemplate call throw a 404 error?

Given this code: ResponseEntity response = testRestTemplate.getForEntity("/api/data", String.class); The server returns 404 Not Found. What is the most likely cause?

A The server is down during the test.

B The testRestTemplate is not autowired correctly.

C The response type String.class is invalid for getForEntity.

D The endpoint /api/data is not mapped in the controller.

💡 Hint

404 means resource not found on server.

A 404 error means the requested URL is not mapped to any controller method. Other options cause different errors or exceptions.

🧠 Conceptual

expert

What is the main advantage of using TestRestTemplate in full integration tests?

Why do developers prefer TestRestTemplate for full integration testing of Spring Boot REST APIs instead of mocking controllers?

A It allows testing controller methods without starting the server.

B It automatically mocks all dependencies for faster tests.

C It tests the entire HTTP stack including serialization, filters, and controller logic in a running server.

D It only tests the service layer without HTTP involvement.

💡 Hint

Think about what full integration means versus unit testing.

TestRestTemplate sends real HTTP requests to a running Spring Boot server, testing serialization, filters, security, and controller logic together. Mocking skips many layers.

Practice

1. What is the main purpose of TestRestTemplate in a Spring Boot application?

easy

A. To perform real HTTP requests for full integration testing

B. To mock database calls during unit tests

C. To replace the main application context

D. To generate API documentation automatically

Solution

1. Step 1: Understand TestRestTemplate's role

   TestRestTemplate is designed to send HTTP requests to the running Spring Boot app during tests.

2. Step 2: Compare with other testing tools

   Unlike mocks or stubs, it tests the full app stack by making real HTTP calls.

3. Final Answer:

   To perform real HTTP requests for full integration testing -> Option A

4. Quick Check:

   TestRestTemplate = real HTTP requests [OK]

Hint: Remember: TestRestTemplate tests full app via HTTP [OK]

Common Mistakes:

• Confusing TestRestTemplate with mocking tools
• Thinking it replaces application context
• Assuming it auto-generates docs

2. Which annotation combination is correct to enable TestRestTemplate with a random port in a Spring Boot test?

easy

A. @SpringBootTest(webEnvironment = WebEnvironment.MOCK)

B. @SpringBootTest(webEnvironment = WebEnvironment.NONE)

C. @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)

D. @SpringBootTest(webEnvironment = WebEnvironment.DEFINED_PORT)

Solution

1. Step 1: Identify webEnvironment for real HTTP tests

   Using RANDOM_PORT starts the server on a random port for real HTTP calls.

2. Step 2: Understand other options

   NONE disables web environment, MOCK uses mock servlet environment, DEFINED_PORT uses fixed port.

3. Final Answer:

   @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT) -> Option C

4. Quick Check:

   RANDOM_PORT enables real HTTP server [OK]

Hint: Use RANDOM_PORT for real HTTP server in tests [OK]

Common Mistakes:

• Using MOCK disables real HTTP server
• Choosing NONE disables web environment
• Assuming DEFINED_PORT is random

3. Given this test snippet using TestRestTemplate:

var response = restTemplate.getForEntity("/api/greet", String.class);
System.out.println(response.getStatusCodeValue());
System.out.println(response.getBody());

If the endpoint /api/greet returns HTTP 200 and body "Hello!", what will be printed?

medium

A. 200\nnull

B. 404\nNot Found

C. 500\nInternal Server Error

D. 200\nHello!

Solution

1. Step 1: Understand getForEntity behavior

   It sends GET request and returns response with status and body.

2. Step 2: Match expected endpoint response

   The endpoint returns 200 status and "Hello!" body, so these print exactly.

3. Final Answer:

   200\nHello! -> Option D

4. Quick Check:

   Status 200 and body "Hello!" printed [OK]

Hint: Response status and body print as returned by endpoint [OK]

Common Mistakes:

• Assuming 404 if endpoint not found in test
• Expecting null body when response is valid
• Confusing status code with body content

4. Consider this test code snippet:

@Autowired
private TestRestTemplate restTemplate;

@Test
public void testGetUser() {
  var response = restTemplate.getForEntity("/users/1", User.class);
  assertEquals(200, response.getStatusCodeValue());
}

If the test fails with a NullPointerException on restTemplate.getForEntity, what is the most likely cause?

medium

A. The test method is missing @Test annotation

B. TestRestTemplate was not injected because @SpringBootTest annotation is missing

C. User class is not serializable

D. The endpoint /users/1 does not exist

Solution

1. Step 1: Identify cause of NullPointerException

   NullPointerException on restTemplate means it was never set (null).

2. Step 2: Check test setup annotations

   Without @SpringBootTest, Spring does not create context or inject beans like TestRestTemplate.

3. Final Answer:

   TestRestTemplate was not injected because @SpringBootTest annotation is missing -> Option B

4. Quick Check:

   Missing @SpringBootTest causes null injection [OK]

Hint: NullPointer on restTemplate means missing @SpringBootTest [OK]

Common Mistakes:

• Blaming missing endpoint for NullPointerException
• Assuming serialization error causes NPE
• Forgetting to add @Test annotation

5. You want to write a full integration test using TestRestTemplate that posts JSON data to /api/items and verifies the created item's ID is returned. Which code snippet correctly performs this test?

hard

A. var item = new Item(null, "Book");
var response = restTemplate.postForEntity("/api/items", item, Item.class);
assertEquals(201, response.getStatusCodeValue());
assertNotNull(response.getBody().getId());

B. var item = new Item(null, "Book");
var response = restTemplate.getForEntity("/api/items", Item.class);
assertEquals(201, response.getStatusCodeValue());

C. var item = new Item(null, "Book");
var response = restTemplate.postForObject("/api/items", item, Item.class);
assertEquals(404, response.getStatusCodeValue());

D. var item = new Item(null, "Book");
var response = restTemplate.exchange("/api/items", HttpMethod.GET, null, Item.class);
assertEquals(201, response.getStatusCodeValue());

Solution

1. Step 1: Identify correct HTTP method for creating resource

   POST is used to create new items, so postForEntity is appropriate.

2. Step 2: Verify response status and body

   201 status means created; response body should contain new item's ID, so assertNotNull on getId() is correct.

3. Final Answer:

   Code snippet using postForEntity with POST and checking 201 and ID -> Option A

4. Quick Check:

   POST + 201 + returned ID = correct test [OK]

Hint: Use postForEntity and check 201 plus returned ID [OK]

Common Mistakes:

• Using GET instead of POST for creation
• Expecting 404 instead of 201 status
• Using postForObject without status check