Add support for strict JSON comparison in WebTestClient

Prior to this commit, WebTestClient only supported "lenient" comparison
of the expected JSON body.

This commit introduces an overloaded variant of `json()` in the
BodyContentSpec that accepts an additional boolean flag to specify
whether a "strict" comparison should be performed.

This new feature is analogous to the existing support in MockMvc.

Closes gh-27993

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

@@ -659,10 +659,10 @@ class DefaultWebTestClient implements WebTestClient {
 		}
 
 		@Override
-		public BodyContentSpec json(String json) {
+		public BodyContentSpec json(String json, boolean strict) {
 			this.result.assertWithDiagnostics(() -> {
 				try {
-					new JsonExpectationsHelper().assertJsonEqual(json, getBodyAsString());
+					new JsonExpectationsHelper().assertJsonEqual(json, getBodyAsString(), strict);
 				}
 				catch (Exception ex) {
 					throw new AssertionError("JSON parsing error", ex);

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

@@ -979,7 +979,24 @@ public interface WebTestClient {
 		 * on to be on the classpath.
 		 * @param expectedJson the expected JSON content.
 		 */
-		BodyContentSpec json(String expectedJson);
+		default BodyContentSpec json(String expectedJson) {
+			return json(expectedJson, false);
+		}
+
+		/**
+		 * Parse the expected and actual response content as JSON and perform a
+		 * comparison in two modes, depending on {@code strict} parameter value, verifying the same attribute-value pairs.
+		 * <ul>
+		 * <li>{@code true}: strict checking.
+		 * <li>{@code false}: lenient checking.
+		 * </ul>
+		 * <p>Use of this option requires the
+		 * <a href="https://jsonassert.skyscreamer.org/">JSONassert</a> library
+		 * on to be on the classpath.
+		 * @param expectedJson the expected JSON content.
+		 * @param strict enables strict checking
+		 */
+		BodyContentSpec json(String expectedJson, boolean strict);
 
 		/**
 		 * Parse expected and actual response content as XML and assert that

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

@@ -31,10 +31,10 @@ import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.hamcrest.Matchers.containsString;
 
 
-
 /**
  * Samples of tests using {@link WebTestClient} with serialized JSON content.
  *
@@ -49,13 +49,32 @@ public class JsonContentTests {
 
 	@Test
 	public void jsonContent() {
-		this.client.get().uri("/persons")
+		this.client.get().uri("/persons/extended")
 				.accept(MediaType.APPLICATION_JSON)
 				.exchange()
 				.expectStatus().isOk()
 				.expectBody().json("[{\"name\":\"Jane\"},{\"name\":\"Jason\"},{\"name\":\"John\"}]");
 	}
 
+	@Test
+	public void jsonContentStrictFail() {
+		assertThatExceptionOfType(AssertionError.class).isThrownBy(() -> this.client.get().uri("/persons/extended")
+				.accept(MediaType.APPLICATION_JSON)
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody().json("[{\"name\":\"Jane\"},{\"name\":\"Jason\"},{\"name\":\"John\"}]", true)
+		);
+	}
+
+	@Test
+	public void jsonContentStrict() {
+		this.client.get().uri("/persons/extended")
+				.accept(MediaType.APPLICATION_JSON)
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody().json("[{\"name\":\"Jane\",\"surname\":\"Williams\"},{\"name\":\"Jason\",\"surname\":\"Johnson\"},{\"name\":\"John\",\"surname\":\"Smith\"}]", true);
+	}
+
 	@Test
 	public void jsonPathIsEqualTo() {
 		this.client.get().uri("/persons")
@@ -98,6 +117,11 @@ public class JsonContentTests {
 			return Flux.just(new Person("Jane"), new Person("Jason"), new Person("John"));
 		}
 
+		@GetMapping("/extended")
+		Flux<ExtendedPerson> getExtendedPersons() {
+			return Flux.just(new ExtendedPerson("Jane", "Williams"), new ExtendedPerson("Jason", "Johnson"), new ExtendedPerson("John", "Smith"));
+		}
+
 		@GetMapping("/{name}")
 		Person getPerson(@PathVariable String name) {
 			return new Person(name);
@@ -109,4 +133,22 @@ public class JsonContentTests {
 		}
 	}
 
+	static class ExtendedPerson {
+		private String name;
+		private String surname;
+
+		public ExtendedPerson(String name, String surname) {
+			this.name = name;
+			this.surname = surname;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public String getSurname() {
+			return surname;
+		}
+	}
+
 }