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

Author: elgleidson

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

@@ -659,10 +659,10 @@ public EntityExchangeResult<Void> isEmpty() {
 }
 
 @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 @@ interface BodyContentSpec {
  * 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.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 @@ Flux<Person> getPersons() {
 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 @@ ResponseEntity<String> savePerson(@RequestBody Person person) {
 }
 }
 
+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;
+}
+}
+
 }