How to use random port for JUNIT Testcases using Spring Boot 1.4.0 +
<p>I am using spring boot 1.3.6 and my JUNIT Test cases are running fine, after upgrading to spring boot 1.4.0 and attempting to remove deprecated classes is throwing me error</p>

<p><strong>My JUNITCLASS with 1.3.x</strong></p>

<pre><code>@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
@WebAppConfiguration
@IntegrationTest({"server.port=0"})
public class CustomerControllerIT {

    @Value("${local.server.port}")
    private int port;
    private URL base;
    private RestTemplate template;

    @Autowired
    private DataBuilder dataBuilder;

    @Autowired
    private CustomerRepository customerRepository;

    private static final String JSON_CONTENT_TYPE = "application/json;charset=UTF-8"; 


    @Before
    public void setUp() throws Exception {
        this.base = new URL("http://localhost:" + port + "/rest/customers");
        template = new TestRestTemplate();      

        /* remove and reload test data */
        customerRepository.deleteAll();     
        dataBuilder.createCustomers().forEach(customer -&gt; customerRepository.save(customer));       
    }

    @Test
    public void getAllCustomers() throws Exception {
        ResponseEntity&lt;String&gt; response = template.getForEntity(base.toString(), String.class);     
        assertThat(response.getStatusCode(), equalTo(HttpStatus.OK));

        List&lt;Customer&gt; customers = convertJsonToCustomers(response.getBody());      
        assertThat(customers.size(), equalTo(3));       
    }

private List&lt;Customer&gt; convertJsonToCustomers(String json) throws Exception        {        
    ObjectMapper mapper = new ObjectMapper();
    return mapper.readValue(json, TypeFactory.defaultInstance().constructCollectionType(List.class, Customer.class));
}
}
</code></pre>

<p><strong>MyClass with 1.4.0</strong></p>

<p>Updates done</p>

<ul>
<li>Removed deprecated TestRestTemplate with spring suggested one</li>
<li>Running with SpringRunner instead of SpringJUnit4ClassRunner</li>
<li>Replaced @SpringApplicationConfiguration(classes = Application.class) with @SpringBootTest(classes = Application.class , webEnvironment=WebEnvironment.RANDOM_PORT)</li>
</ul>

<p>After Changes</p>

<pre><code>@RunWith(SpringRunner.class)
@SpringBootTest(classes = Application.class , webEnvironment=WebEnvironment.RANDOM_PORT)
@WebAppConfiguration
public class CustomerControllerIT {

    @Value("${local.server.port}")
    private int port;
    private URL base;
    private TestRestTemplate template;

    @Autowired
    private DataBuilder dataBuilder;

    @Autowired
    private CustomerRepository customerRepository;

    private static final String JSON_CONTENT_TYPE = "application/json;charset=UTF-8"; 


    @Before
    public void setUp() throws Exception {
        this.base = new URL("http://localhost:" + port + "/rest/customers");
        template = new TestRestTemplate();      

        /* remove and reload test data */
        customerRepository.deleteAll();     
        dataBuilder.createCustomers().forEach(customer -&gt; customerRepository.save(customer));       
    }
}
</code></pre>

<p>Now I am receiving NPE when i try to run JUNIT Testcase, How can I set the random port to make my JUNIT test case running in Spring Boot 1.4.0 +?</p>

<p><strong>Update :</strong></p>

<p>Here is the stacktrace of the issue</p>

<pre><code>java.lang.IllegalStateException: Failed to load ApplicationContext
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124)
    at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:83)
    at org.springframework.test.context.web.ServletTestExecutionListener.setUpRequestContextIfNecessary(ServletTestExecutionListener.java:189)
    at org.springframework.test.context.web.ServletTestExecutionListener.prepareTestInstance(ServletTestExecutionListener.java:131)
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:230)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:228)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:287)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:289)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:247)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: java.lang.NullPointerException
    at org.springframework.test.context.web.socket.MockServerContainerContextCustomizer.customizeContext(MockServerContainerContextCustomizer.java:38)
    at org.springframework.boot.test.context.SpringBootContextLoader$ContextCustomizerAdapter.initialize(SpringBootContextLoader.java:270)
    at org.springframework.boot.SpringApplication.applyInitializers(SpringApplication.java:633)
    at org.springframework.boot.SpringApplication.prepareContext(SpringApplication.java:347)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:311)
    at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:111)
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:98)
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:116)
    ... 25 more
</code></pre>