How to mock REST service response on the client side?

Question

I would like to mock the RESTEasy client response in my JUnit tests with response body from the content in predefined xml-files. Consider following Person service client API and Person entity:

package my.company.com;

import java.net.URI;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;

import org.apache.http.auth.AuthScope;
import org.apache.http.auth.Credentials;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CookieStore;
import org.apache.http.client.protocol.ClientContext;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.jboss.resteasy.client.ClientRequest;
import org.jboss.resteasy.client.ClientResponse;
import org.jboss.resteasy.client.core.executors.ApacheHttpClient4Executor;

public class PersonServiceClient {
    private final DefaultHttpClient httpClient;

public PersonServiceClient(String username, String password) {
    Credentials credentials = new UsernamePasswordCredentials(username, password);
    httpClient = new DefaultHttpClient();
    httpClient.getCredentialsProvider().setCredentials(AuthScope.ANY, credentials);
}

public Person[] getPersons() throws Exception
{
    URI url = new URI("http://www.mycompany.com/persons/");
    Person[] persons = getByRest(url, Person[].class);
    return persons;
}

private <T> T getByRest(URI url, Class<T> returnType) throws Exception {
    ClientRequest client = createClientRequest(url.toString());
    ClientResponse<T> response = client.get(returnType);
    return response.getEntity();
}

private ClientRequest createClientRequest(String url) {
    // Storing cookie to avoid creating new client for every call
    CookieStore cookieStore = new BasicCookieStore();
    HttpContext httpContext = new BasicHttpContext();
    httpContext.setAttribute(ClientContext.COOKIE_STORE, cookieStore);
    ApacheHttpClient4Executor clientExecutor = new ApacheHttpClient4Executor(httpClient, httpContext);

    ClientRequest clientRequest = new ClientRequest(url, clientExecutor);
    return clientRequest;
}

@XmlRootElement(name = "resource")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {
    private String type;
    private String name;
    private String addres;
    private String phone;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type= type;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddres() {
        return addres;
    }

    public void setAddres(String addres) {
        this.addres = addres;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public Person() {
    }
}
}

and the content of response-test1.xml:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<collection>
    <resource>
        <type>Peson</type>
        <name>Christopher Monroe</name>
        <addres>Wall Street 2</addres>
        <phone>12345678</<phone>
    </resource>
    <resource>
        <type>Person</type>
        <name>John Dee</name>
        <addres>Down town 2</addres>
        <phone>2997562123</phone>
    </resource>
</collection>

How can I mock the body of response in JUnit test below with content from response-test.xml file above?

@Test
public void testGetPersons() throws Exception{
    PersonServiceClient client = new PersonServiceClient("joe", "doe");
    Person[] persons = client.getPersons();
}

I tried to follow example in this post Is there a client-side mock framework for RESTEasy? but it doesn't show exactly how to select response body.

Answer 1

Rather than mocking the RESTEasy client, I'd suggest mocking the server using WireMock (disclaimer - I wrote it): http://wiremock.org/

It's configurable via a fluent Java API from within JUnit and runs up an embedded web server which serves stubbed responses and permits you to verify the requests sent from your app.

I've written about the rationale for not mocking HTTP clients in a bit more detail here: Introducing WireMock

Answer 2

Consider using a factory to create the ClientRequest then mock the factory to return a mock of ClientRequest.