How can I use MockWebServer for Junit test cases of webclient? - unit-testing

Question

I have a spring-boot application which calls some third party URL (let's say http://example.com/someUri) using webclient(I have used application-dev.properties for injecting this url in my application to achieve loose coupling) and consumes the response and use it in my application.
It's my first time when I am going to write test cases for webclient. and there I used #SprintBootTest.
I found that there are two ways where I can test my webclient with third party Api call by mocking the api call and make it call to my local url(which will be using url(http://localhost:{portNumber}/someUri) from my testing properties file: src/test/resources/application.properties) where It will be giving some mockedResponse in return to my real client:
Using wiremock
Using MockWebServer
consider above code for better understanding:
#Service
Class SampleService{
#Value("${sample.url}")
private String sampleUrl;
public String dummyClient() {
String sample =webClient.get()
.uri(sampleUrl)
.header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
.retrieve()
.bodyToMono(String.class)
.block();
return sample;
}
}
application-dev.properties:
sample.url:http://example.com/someUri
src/test/resouces/application.properties:
http://localhost:8090/someUri
Testing class:
#SpringBootTest
public class sampleTestingClass {
#Autowired
private SampleService sampleService;
#Value("${sample.url}")
private String sampleUrl;
public static MockWebServer mockWebServer = new MockWebServer();
#BeforeAll
static void setUp() throws IOException {
mockWebServer.start(8090);
}
#AfterAll
static void tearUp() throws IOException {
mockWebServer.close();
}
HttpUrl url = mockWebServer.url("/someUri");
mockWebServer
.enqueue(
new MockResponse()
.setResponseCode(200)
.setHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
.setBody("Sample Successful"));
String sample = sampleService.dummyClient();
assertEquals(sample ,matches("Sample Successful"));
}
}
but this code isn't working. it's giving me above error:
java.lang.NullPointerException
It will be really helpful if anybody knows how this can be fixed to achieve my unit testing using mocked Url? Thanks in advance!

Answer 1

Here is a working example:
#Component
public class QuotesClient {
private final WebClient webClient;
public QuotesClient(WebClient.Builder builder, #Value("${client.baseUrl}") String baseUrl) {
this.webClient = builder.baseUrl(baseUrl).build();
}
public JsonNode getData() {
return this.webClient
.get()
.retrieve()
.bodyToMono(JsonNode.class)
.block();
}
}
Using the WebClient.Builder is optional.
The corresponding test can look like the following:
class QuotesClientTest {
private QuotesClient quotesClient;
private MockWebServer server;
#BeforeEach
public void setup() {
this.server = new MockWebServer();
this.quotesClient = new QuotesClient(WebClient.builder(), server.url("/").toString());
}
#Test
public void test() {
server.enqueue(new MockResponse()
.setStatus("HTTP/1.1 200")
.setBody("{\"bar\":\"barbar\",\"foo\":\"foofoo\"}")
.addHeader("Content-Type", "application/json"));
JsonNode data = quotesClient.getData();
assertNotNull(data);
System.out.println(data);
}
}
If you are searching for a similar setup using WireMock, Spring Boot, and JUnit 5, take a look at the linked guide.