I/O error on GET request for unkown host in Junit test case
<p>I am writing the Junit test cases for method which uses the rest template, below is the method.</p>

<pre><code>public Student getStudent(Integer studId) throws Exception {
        RestTemplate restTemplate = new RestTemplate(
                        utility.setAuthenticationParameters(
                                "test", "test"));
        String url=https://dev.test.res.com/student;
            HttpHeaders headers = new HttpHeaders();
        HttpEntity&lt;String&gt; entity = new HttpEntity&lt;&gt;(headers);
        url =url+"?"+studId;
        Map&lt;String, String&gt; params = new HashMap&lt;&gt;();
        params.put("studId", studId);
        ResponseEntity&lt;String&gt; response = restTemplate.exchange(url,
                            HttpMethod.GET, entity, String.class, params);
    }
</code></pre>

<p>Junit test cases for the above method I have written using mockito framework</p>

<pre><code>import static org.junit.Assert.*;

import java.io.IOException;
import java.net.URI;
import java.text.ParseException;
import java.util.HashMap;
import java.util.Map;

import javax.xml.datatype.DatatypeConfigurationException;

import junit.framework.Assert;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.MockitoAnnotations;
import org.mockito.runners.MockitoJUnitRunner;
import org.springframework.boot.test.IntegrationTest;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.client.ClientHttpRequest;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.mock.http.client.MockClientHttpRequest;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.web.WebAppConfiguration;
import org.springframework.test.web.client.MockRestServiceServer;
import org.springframework.web.client.RestTemplate;


@RunWith(MockitoJUnitRunner.class)
@ContextConfiguration(classes = {ConfigData.class})
public class StudentClientTest {

    @Mock
    RestTemplate restTemplate;

    @Mock
    ClientHttpRequestFactory requestFactory;

    @Mock
    ClientHttpRequest request;

    @Mock
    MockClientHttpRequest mockClientHttpRequest;

    @Mock
    ClientHttpResponse response;

    @Mock
    ResponseEntity&lt;String&gt; responseEntory;

    private MockRestServiceServer mockServer;


    @InjectMocks
    private StudentClient studentClient= new StudentClient();



    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);

    }


    @Test
    public void getStudentTest() throws Exception{



        String uri = "https://dev.test.res.com/student?";

        Integer studId=100;
        uri=uri+studId;

        Mockito.when(restTemplate.exchange(Mockito.contains(uri),Mockito.eq(HttpMethod.GET),Mockito.isA(HttpEntity.class), Mockito.eq(String.class),Mockito.isNotNull())).thenReturn(responseEntory);
        assertNotNull(studentClient.getStudent(100));
}


}
</code></pre>

<p>I/O error on GET request for "<a href="https://dev.test.res.com/student?studId=100" rel="nofollow">https://dev.test.res.com/student?studId=100</a>": nested exception is java.net.UnknownHostException: dev.test.res.com</p>

<p>I have mocked the object but still is failing with exception</p>