TestRestTemplate for API testing in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a TestRestTemplate instance.

JUnit

TestRestTemplate restTemplate = new [1]();

Drag options to blanks, or click blank then click option'

ATestRestTemplate

BRestTemplate

CHttpClient

DWebClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using RestTemplate instead of TestRestTemplate.

Using HttpClient or WebClient which are not part of Spring Boot test utilities.

The TestRestTemplate class is used to create a test client for API testing in Spring Boot.

2fill in blank

medium

Complete the code to send a GET request to '/api/users' and get the response as a String.

JUnit

ResponseEntity<String> response = restTemplate.[1]("/api/users", String.class);

Drag options to blanks, or click blank then click option'

ApostForEntity

Bexchange

Cdelete

DgetForEntity

Attempts:

3 left

💡 Hint

Common Mistakes

Using postForEntity which sends a POST request.

Using delete which sends a DELETE request.

Using exchange without specifying HTTP method.

The getForEntity method sends a GET request and returns the response wrapped in a ResponseEntity.

3fill in blank

hard

Fix the error in the assertion to check if the response status code is 200 OK.

JUnit

assertEquals(HttpStatus.[1], response.getStatusCode());

Drag options to blanks, or click blank then click option'

AOK

BNOT_FOUND

CBAD_REQUEST

DCREATED

Attempts:

3 left

💡 Hint

Common Mistakes

Using NOT_FOUND (404) or BAD_REQUEST (400) which indicate errors.

Using CREATED (201) which is for resource creation.

The status code HttpStatus.OK corresponds to HTTP 200, which means the request was successful.

4fill in blank

hard

Fill both blanks to send a POST request with a User object and receive a User response.

JUnit

ResponseEntity<User> response = restTemplate.[1]("/api/users", [2], User.class);

Drag options to blanks, or click blank then click option'

ApostForEntity

BgetForEntity

Cnew User("John", "[e-mail]")

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using getForEntity for POST requests.

Passing null instead of a User object.

The postForEntity method sends a POST request. The second argument is the User object to send in the request body.

5fill in blank

hard

Fill all three blanks to assert the response body has the expected user's email.

JUnit

assertTrue(response.getBody().[1]().[2]("[3]"));

Drag options to blanks, or click blank then click option'

AgetEmail

Bequals

[e-mail]

DtoString

Attempts:

3 left

💡 Hint

Common Mistakes

Using toString instead of getEmail.

Using '==' instead of equals for string comparison.

Using wrong field name.

We call getEmail() on the User object, then check if it equals the expected email string.

Practice

1. What is the primary purpose of TestRestTemplate in JUnit testing?

easy

A. To mock database connections during tests

B. To send real HTTP requests to test REST APIs

C. To generate random test data for unit tests

D. To create UI components for testing

Solution

1. Step 1: Understand the role of TestRestTemplate

   TestRestTemplate is designed to send actual HTTP requests to REST APIs during integration tests.

2. Step 2: Compare with other options

   Mocking databases, generating test data, or creating UI components are unrelated to TestRestTemplate's purpose.

3. Final Answer:

   To send real HTTP requests to test REST APIs -> Option B

4. Quick Check:

   TestRestTemplate = Real HTTP requests [OK]

Hint: Remember: TestRestTemplate sends real HTTP calls [OK]

Common Mistakes:

• Confusing TestRestTemplate with mocking tools
• Thinking it generates test data
• Assuming it tests UI components

2. Which of the following is the correct way to autowire TestRestTemplate in a Spring Boot test class?

easy

A. @Autowired private TestRestTemplate restTemplate;

B. private TestRestTemplate restTemplate = new TestRestTemplate();

C. @InjectMocks private TestRestTemplate restTemplate;

D. private TestRestTemplate restTemplate = null;

Solution

1. Step 1: Identify correct Spring Boot injection

   In Spring Boot tests, @Autowired is used to inject TestRestTemplate automatically.

2. Step 2: Evaluate other options

   Creating a new instance manually or using @InjectMocks is incorrect for TestRestTemplate injection in Spring Boot tests.

3. Final Answer:

   @Autowired private TestRestTemplate restTemplate; -> Option A

4. Quick Check:

   Use @Autowired for TestRestTemplate injection [OK]

Hint: Use @Autowired to inject TestRestTemplate [OK]

Common Mistakes:

• Manually instantiating TestRestTemplate
• Using @InjectMocks instead of @Autowired
• Leaving the variable null without injection

3. Given the following test code snippet using TestRestTemplate:

ResponseEntity<String> response = restTemplate.getForEntity("/api/users/1", String.class);
int statusCode = response.getStatusCodeValue();
String body = response.getBody();

If the API returns HTTP 200 with body "User Found", what will be the values of statusCode and body?

medium

A. statusCode = 404, body = null

B. statusCode = 500, body = "Error"

C. statusCode = 200, body = "User Found"

D. statusCode = 200, body = null

Solution

1. Step 1: Understand getForEntity behavior

   getForEntity sends a GET request and returns the full response including status and body.

2. Step 2: Match API response to variables

   Since API returns 200 and "User Found", statusCode will be 200 and body will be "User Found".

3. Final Answer:

   statusCode = 200, body = "User Found" -> Option C

4. Quick Check:

   API 200 + body = statusCode 200 & body "User Found" [OK]

Hint: getForEntity returns status and body as received [OK]

Common Mistakes:

• Assuming body is null on success
• Confusing status codes with error codes
• Ignoring response body content

4. Consider this test code using TestRestTemplate:

@Autowired
private TestRestTemplate restTemplate;

@Test
public void testGetUser() {
    ResponseEntity<String> response = restTemplate.getForEntity("/api/users/", String.class);
    assertEquals(200, response.getStatusCodeValue());
}

What is the likely problem with this test?

medium

A. The URL is missing a user ID, causing a 404 error

B. The assertion should check for 404 instead of 200

C. TestRestTemplate cannot be autowired

D. ResponseEntity<String> is not a valid return type

Solution

1. Step 1: Analyze the request URL

   The URL "/api/users/" lacks a specific user ID, so the endpoint may not exist or return a list, not a single user.

2. Step 2: Understand the assertion failure cause

   Expecting status 200 for a missing user ID endpoint may cause a 404 error, failing the test.

3. Final Answer:

   The URL is missing a user ID, causing a 404 error -> Option A

4. Quick Check:

   Missing ID in URL causes 404, not 200 [OK]

Hint: Check URL completeness before asserting status [OK]

Common Mistakes:

• Assuming URL without ID returns 200
• Wrong assertion status code
• Thinking autowiring is the issue

5. You want to test a POST API endpoint /api/users that creates a user and returns HTTP 201 with the created user JSON. Which TestRestTemplate method and assertion combination correctly tests this?

hard

A. Use delete with user ID, then assert status 204

B. Use getForEntity with user ID, then assert status 200

C. Use exchange with GET method, then assert status 404

D. Use postForEntity with user object, then assert status 201 and response body contains user data

Solution

1. Step 1: Identify correct HTTP method for creation

   POST is used to create resources, so postForEntity is appropriate for sending the user object.

2. Step 2: Validate expected response and assertions

   The API returns 201 Created with user JSON, so assert status 201 and check response body contains user data.

3. Final Answer:

   Use postForEntity with user object, then assert status 201 and response body contains user data -> Option D

4. Quick Check:

   POST + postForEntity + assert 201 + check body [OK]

Hint: POST creation uses postForEntity and assert 201 [OK]

Common Mistakes:

• Using GET instead of POST for creation
• Asserting wrong status codes
• Ignoring response body validation