Merge pull request #6706 from Maciej Walkowiak

* gh-6706:
  Polish “Add constructor to TestRestTemplate that takes a RestTemplateBuilder”
  Add constructor to TestRestTemplate that takes a RestTemplateBuilder

spring-boot-test/src/main/java/org/springframework/boot/test/web/client/TestRestTemplate.java

@@ -82,6 +82,16 @@ public class TestRestTemplate {
 
 	private final RestTemplate restTemplate;
 
+	/**
+	 * Create a new {@link TestRestTemplate} instance.
+	 * @param restTemplateBuilder builder used to configure underlying
+	 * {@link RestTemplate}
+	 * @since 1.4.1
+	 */
+	public TestRestTemplate(RestTemplateBuilder restTemplateBuilder) {
+		this(buildRestTemplate(restTemplateBuilder));
+	}
+
 	/**
 	 * Create a new {@link TestRestTemplate} instance.
 	 * @param httpClientOptions client options to use if the Apache HTTP Client is used
@@ -117,6 +127,12 @@ public class TestRestTemplate {
 		this.restTemplate = restTemplate;
 	}
 
+	private static RestTemplate buildRestTemplate(
+			RestTemplateBuilder restTemplateBuilder) {
+		Assert.notNull(restTemplateBuilder, "RestTemplateBuilder must not be null");
+		return restTemplateBuilder.build();
+	}
+
 	private void addAuthentication(RestTemplate restTemplate, String username,
 			String password) {
 		if (username == null) {

spring-boot-test/src/test/java/org/springframework/boot/test/web/client/TestRestTemplateTests.java

@@ -24,6 +24,7 @@ import org.junit.Test;
 
 import org.springframework.boot.test.web.client.TestRestTemplate.CustomHttpComponentsClientHttpRequestFactory;
 import org.springframework.boot.test.web.client.TestRestTemplate.HttpClientOption;
+import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.http.client.InterceptingClientHttpRequestFactory;
@@ -33,6 +34,7 @@ import org.springframework.web.client.RestOperations;
 import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 
 /**
@@ -43,6 +45,14 @@ import static org.mockito.Mockito.mock;
  */
 public class TestRestTemplateTests {
 
+	@Test
+	public void fromRestTemplateBuilder() {
+		RestTemplateBuilder builder = mock(RestTemplateBuilder.class);
+		RestTemplate delegate = new RestTemplate();
+		given(builder.build()).willReturn(delegate);
+		assertThat(new TestRestTemplate(builder).getRestTemplate()).isEqualTo(delegate);
+	}
+
 	@Test
 	public void simple() {
 		// The Apache client is on the classpath so we get the fully-fledged factory