Allow LocalHostUriTemplateHandler to be created with a custom underlying UriTemplateHandler

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

@@ -58,9 +58,23 @@ public LocalHostUriTemplateHandler(Environment environment) {
 	 * @since 1.4.1
 	 */
 	public LocalHostUriTemplateHandler(Environment environment, String scheme) {
-		super(new DefaultUriBuilderFactory());
+		this(environment, scheme, new DefaultUriBuilderFactory());
+	}
+
+	/**
+	 * Create a new {@code LocalHostUriTemplateHandler} that will generate URIs with the
+	 * given {@code scheme}, use the given {@code environment} to determine the
+	 * context-path and port and delegate to the given template {@code handler}.
+	 * @param environment the environment used to determine the port
+	 * @param scheme the scheme of the root uri
+	 * @param handler the delegate handler
+	 * @since 2.0.3
+	 */
+	public LocalHostUriTemplateHandler(Environment environment, String scheme, UriTemplateHandler handler) {
+		super(handler);
 		Assert.notNull(environment, "Environment must not be null");
 		Assert.notNull(scheme, "Scheme must not be null");
+		Assert.notNull(handler, "Handler must not be null");
 		this.environment = environment;
 		this.scheme = scheme;
 	}

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

@@ -50,6 +50,13 @@ public void createWhenSchemeIsNullShouldThrowException() {
 		new LocalHostUriTemplateHandler(new MockEnvironment(), null);
 	}
 
+	@Test
+	public void createWhenHandlerIsNullShouldThrowException() {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Handler must not be null");
+		new LocalHostUriTemplateHandler(new MockEnvironment(), "http", null);
+	}
+
 	@Test
 	public void getRootUriShouldUseLocalServerPort() {
 		MockEnvironment environment = new MockEnvironment();