Allow empty path in MockMvc

Closes gh-28823

spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -148,7 +148,7 @@ public class MockHttpServletRequestBuilder
 
 	private static URI initUri(String url, Object[] vars) {
 		Assert.notNull(url, "'url' must not be null");
-		Assert.isTrue(url.startsWith("/") || url.startsWith("http://") || url.startsWith("https://"), "" +
+		Assert.isTrue(url.isEmpty() || url.startsWith("/") || url.startsWith("http://") || url.startsWith("https://"),
 				"'url' should start with a path or be a complete HTTP URL: " + url);
 		return UriComponentsBuilder.fromUriString(url).buildAndExpand(vars).encode().toUri();
 	}

spring-test/src/test/java/org/springframework/test/web/reactive/server/DefaultControllerSpecTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,15 @@ public class DefaultControllerSpecTests {
 				.expectBody(String.class).isEqualTo("Success");
 	}
 
+	@Test
+	public void controllerEmptyPath() {
+		new DefaultControllerSpec(new MyController()).build()
+				.get().uri("")
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody(String.class).isEqualTo("Success empty path");
+	}
+
 	@Test
 	public void controllerAdvice() {
 		new DefaultControllerSpec(new MyController())
@@ -116,10 +125,15 @@ public class DefaultControllerSpecTests {
 	private static class MyController {
 
 		@GetMapping("/")
-		public String handle() {
+		public String handleRootPath() {
 			return "Success";
 		}
 
+		@GetMapping
+		public String handleEmptyPath() {
+			return "Success empty path";
+		}
+
 		@GetMapping("/exception")
 		public void handleWithError() {
 			throw new IllegalStateException();

spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -165,6 +165,17 @@ class MockHttpServletRequestBuilderTests {
 		assertThat(request.getPathInfo()).isNull();
 	}
 
+	@Test // gh-28823
+	void emptyPath() {
+		this.builder = new MockHttpServletRequestBuilder(HttpMethod.GET, "");
+		MockHttpServletRequest request = this.builder.buildRequest(this.servletContext);
+
+		assertThat(request.getRequestURI()).isEqualTo("");
+		assertThat(request.getContextPath()).isEqualTo("");
+		assertThat(request.getServletPath()).isEqualTo("");
+		assertThat(request.getPathInfo()).isNull();
+	}
+
 	@Test // SPR-16453
 	void pathInfoIsDecoded() {
 		this.builder = new MockHttpServletRequestBuilder(HttpMethod.GET, "/travel/hotels 42");