Remove TestRestTemplate constructors taking template args

As discussed in gh-11872, `TestRestTemplate` constructor variants taking
a `RestTemplate` argument are confusing since the main goal of that
class is to mutate `RestTemplate`.

This commit removes all those constructor variants and replaces them
with `RestTemplateBuilder` arguments when possible.

Closes gh-11872

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/spock/SpockTestRestTemplateExample.java

@@ -46,7 +46,7 @@ public class SpockTestRestTemplateExample {
 				Environment environment) {
 			RestTemplateBuilder builder = builderProvider.getIfAvailable();
 			TestRestTemplate template = builder == null ? new TestRestTemplate()
-					: new TestRestTemplate(builder.build());
+					: new TestRestTemplate(builder);
 			template.setUriTemplateHandler(new LocalHostUriTemplateHandler(environment));
 			return template;
 		}

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

@@ -94,7 +94,7 @@ public class TestRestTemplate {
 	 * @since 1.4.1
 	 */
 	public TestRestTemplate(RestTemplateBuilder restTemplateBuilder) {
-		this(buildRestTemplate(restTemplateBuilder));
+		this(restTemplateBuilder, null, null);
 	}
 
 	/**
@@ -113,14 +113,24 @@ public class TestRestTemplate {
 	 */
 	public TestRestTemplate(String username, String password,
 			HttpClientOption... httpClientOptions) {
-		this(new RestTemplate(), username, password, httpClientOptions);
+		this(new RestTemplateBuilder(), username, password, httpClientOptions);
 	}
 
-	public TestRestTemplate(RestTemplate restTemplate) {
-		this(restTemplate, null, null);
+	/**
+	 * Create a new {@link TestRestTemplate} instance with the specified credentials.
+	 * @param restTemplateBuilder builder used to configure underlying
+	 * {@link RestTemplate}
+	 * @param username the username to use (or {@code null})
+	 * @param password the password (or {@code null})
+	 * @param httpClientOptions client options to use if the Apache HTTP Client is used
+	 * @since 2.0.0
+	 */
+	public TestRestTemplate(RestTemplateBuilder restTemplateBuilder, String username, String password,
+			HttpClientOption... httpClientOptions) {
+		this(buildRestTemplate(restTemplateBuilder), username, password, httpClientOptions);
 	}
 
-	public TestRestTemplate(RestTemplate restTemplate, String username, String password,
+	private TestRestTemplate(RestTemplate restTemplate, String username, String password,
 			HttpClientOption... httpClientOptions) {
 		Assert.notNull(restTemplate, "RestTemplate must not be null");
 		this.httpClientOptions = httpClientOptions;

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

@@ -143,7 +143,7 @@ class TestRestTemplateTestContextCustomizer implements ContextCustomizer {
 				throws BeansException {
 			RestTemplateBuilder builder = getRestTemplateBuilder(applicationContext);
 			boolean sslEnabled = isSslEnabled(applicationContext);
-			TestRestTemplate template = new TestRestTemplate(builder.build(), null, null,
+			TestRestTemplate template = new TestRestTemplate(builder, null, null,
 					sslEnabled ? SSL_OPTIONS : DEFAULT_OPTIONS);
 			LocalHostUriTemplateHandler handler = new LocalHostUriTemplateHandler(
 					applicationContext.getEnvironment(), sslEnabled ? "https" : "http");

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

@@ -85,7 +85,7 @@ public class TestRestTemplateTests {
 	@Test
 	public void getRootUriRootUriSetViaRestTemplateBuilder() {
 		String rootUri = "http://example.com";
-		RestTemplate delegate = new RestTemplateBuilder().rootUri(rootUri).build();
+		RestTemplateBuilder delegate = new RestTemplateBuilder().rootUri(rootUri);
 		assertThat(new TestRestTemplate(delegate).getRootUri()).isEqualTo(rootUri);
 	}
 
@@ -127,7 +127,9 @@ public class TestRestTemplateTests {
 		RestTemplate delegate = mock(RestTemplate.class);
 		given(delegate.getUriTemplateHandler())
 				.willReturn(new DefaultUriBuilderFactory());
-		final TestRestTemplate restTemplate = new TestRestTemplate(delegate);
+		RestTemplateBuilder builder = mock(RestTemplateBuilder.class);
+		given(builder.build()).willReturn(delegate);
+		final TestRestTemplate restTemplate = new TestRestTemplate(builder);
 		ReflectionUtils.doWithMethods(RestOperations.class, new MethodCallback() {
 
 			@Override
@@ -338,9 +340,8 @@ public class TestRestTemplateTests {
 				.create("http://localhost:8080/a/b/c.txt?param=%7Bsomething%7D");
 		given(requestFactory.createRequest(eq(absoluteUri), any(HttpMethod.class)))
 				.willReturn(request);
-		RestTemplate delegate = new RestTemplate();
-		TestRestTemplate template = new TestRestTemplate(delegate);
-		delegate.setRequestFactory(requestFactory);
+		TestRestTemplate template = new TestRestTemplate();
+		template.getRestTemplate().setRequestFactory(requestFactory);
 		LocalHostUriTemplateHandler uriTemplateHandler = new LocalHostUriTemplateHandler(
 				new MockEnvironment());
 		template.setUriTemplateHandler(uriTemplateHandler);

spring-boot-samples/spring-boot-sample-actuator-custom-security/src/test/java/sample/actuator/customsecurity/CorsSampleActuatorApplicationTests.java

@@ -27,14 +27,13 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.web.client.LocalHostUriTemplateHandler;
 import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.context.ApplicationContext;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
-import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.context.junit4.SpringRunner;
-import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -55,12 +54,11 @@ public class CorsSampleActuatorApplicationTests {
 
 	@Before
 	public void setUp() {
-		RestTemplate restTemplate = new RestTemplate();
+		RestTemplateBuilder builder = new RestTemplateBuilder();
 		LocalHostUriTemplateHandler handler = new LocalHostUriTemplateHandler(
 				this.applicationContext.getEnvironment(), "http");
-		restTemplate.setUriTemplateHandler(handler);
-		restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory());
-		this.testRestTemplate = new TestRestTemplate(restTemplate);
+		builder = builder.uriTemplateHandler(handler);
+		this.testRestTemplate = new TestRestTemplate(builder);
 	}
 
 	@Test