Fix TestRestTemplate request factory management

This commit fixes two issues in `TestRestTemplate`:

* it improves the detection of the underlying request factory, using
reflection to look inside the intercepting request factory if
interceptors were configured

* it avoids reusing the same request factory when creating a new
`TestRestTemplate` with `withBasicAuth`. Sharing the same instance would
result in sharing authentication state (HTTP cookies). Since the
original request factory can't be detected consistently, a new one is
selected automatically

See gh-8697

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

@@ -134,11 +134,17 @@ public TestRestTemplate(RestTemplateBuilder restTemplateBuilder, String username
 				httpClientOptions);
 	}
 
+	private static RestTemplate buildRestTemplate(
+			RestTemplateBuilder restTemplateBuilder) {
+		Assert.notNull(restTemplateBuilder, "RestTemplateBuilder must not be null");
+		return restTemplateBuilder.build();
+	}
+
 	private TestRestTemplate(RestTemplate restTemplate, String username, String password,
 			HttpClientOption... httpClientOptions) {
 		Assert.notNull(restTemplate, "RestTemplate must not be null");
 		this.httpClientOptions = httpClientOptions;
-		if (restTemplate.getRequestFactory().getClass().getName()
+		if (getRequestFactoryClass(restTemplate).getName()
 				.equals("org.springframework.http.client.HttpComponentsClientHttpRequestFactory")) {
 			restTemplate.setRequestFactory(
 					new CustomHttpComponentsClientHttpRequestFactory(httpClientOptions));
@@ -148,10 +154,16 @@ private TestRestTemplate(RestTemplate restTemplate, String username, String pass
 		this.restTemplate = restTemplate;
 	}
 
-	private static RestTemplate buildRestTemplate(
-			RestTemplateBuilder restTemplateBuilder) {
-		Assert.notNull(restTemplateBuilder, "RestTemplateBuilder must not be null");
-		return restTemplateBuilder.build();
+	private Class<? extends ClientHttpRequestFactory> getRequestFactoryClass(RestTemplate restTemplate) {
+		ClientHttpRequestFactory requestFactory = restTemplate.getRequestFactory();
+		if (InterceptingClientHttpRequestFactory.class.isAssignableFrom(requestFactory.getClass())) {
+			Field requestFactoryField = ReflectionUtils
+					.findField(RestTemplate.class, "requestFactory");
+			ReflectionUtils.makeAccessible(requestFactoryField);
+			requestFactory = (ClientHttpRequestFactory)
+					ReflectionUtils.getField(requestFactoryField, restTemplate);
+		}
+		return requestFactory.getClass();
 	}
 
 	private void addAuthentication(RestTemplate restTemplate, String username,
@@ -1022,30 +1034,18 @@ public RestTemplate getRestTemplate() {
 	 * @since 1.4.1
 	 */
 	public TestRestTemplate withBasicAuth(String username, String password) {
-		RestTemplate restTemplate = new RestTemplate();
-		restTemplate.setMessageConverters(getRestTemplate().getMessageConverters());
-		restTemplate.setInterceptors(getRestTemplate().getInterceptors());
-		restTemplate.setRequestFactory(getRequestFactory(getRestTemplate()));
-		restTemplate.setUriTemplateHandler(getRestTemplate().getUriTemplateHandler());
+		RestTemplate restTemplate = new RestTemplateBuilder()
+				.messageConverters(getRestTemplate().getMessageConverters())
+				.interceptors(getRestTemplate().getInterceptors())
+				.uriTemplateHandler(getRestTemplate().getUriTemplateHandler())
+				.build();
 		TestRestTemplate testRestTemplate = new TestRestTemplate(restTemplate, username,
 				password, this.httpClientOptions);
 		testRestTemplate.getRestTemplate()
 				.setErrorHandler(getRestTemplate().getErrorHandler());
 		return testRestTemplate;
 	}
 
-	private ClientHttpRequestFactory getRequestFactory(RestTemplate restTemplate) {
-		ClientHttpRequestFactory requestFactory = restTemplate.getRequestFactory();
-		if (InterceptingClientHttpRequestFactory.class.isAssignableFrom(requestFactory.getClass())) {
-			Field requestFactoryField = ReflectionUtils
-					.findField(RestTemplate.class, "requestFactory");
-			ReflectionUtils.makeAccessible(requestFactoryField);
-			requestFactory = (ClientHttpRequestFactory)
-					ReflectionUtils.getField(requestFactoryField, getRestTemplate());
-		}
-		return requestFactory;
-	}
-
 	@SuppressWarnings({ "rawtypes", "unchecked" })
 	private RequestEntity<?> createRequestEntityWithRootAppliedUri(
 			RequestEntity<?> requestEntity) {