Add support for conversion of the whole JSON document

Closes gh-33018

spring-test/src/main/java/org/springframework/test/json/AbstractJsonContentAssert.java

@@ -18,15 +18,20 @@
 
 import java.io.File;
 import java.io.InputStream;
+import java.lang.reflect.Type;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.util.function.Consumer;
 
 import com.jayway.jsonpath.JsonPath;
 import com.jayway.jsonpath.PathNotFoundException;
+import org.assertj.core.api.AbstractAssert;
 import org.assertj.core.api.AbstractObjectAssert;
+import org.assertj.core.api.AssertFactory;
 import org.assertj.core.api.AssertProvider;
 import org.assertj.core.api.Assertions;
+import org.assertj.core.api.InstanceOfAssertFactories;
 import org.assertj.core.error.BasicErrorMessageFactory;
 import org.assertj.core.internal.Failures;
 
@@ -35,8 +40,12 @@
 import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpInputMessage;
+import org.springframework.http.MediaType;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.lang.Nullable;
+import org.springframework.mock.http.MockHttpInputMessage;
 import org.springframework.util.Assert;
 
 /**
@@ -90,6 +99,62 @@ protected AbstractJsonContentAssert(@Nullable JsonContent actual, Class<?> selfT
 		as("JSON content");
 	}
 
+	/**
+	 * Verify that the actual value can be converted to an instance of the
+	 * given {@code target}, and produce a new {@linkplain AbstractObjectAssert
+	 * assertion} object narrowed to that type.
+	 * @param target the {@linkplain Class type} to convert the actual value to
+	 */
+	public <T> AbstractObjectAssert<?, T> convertTo(Class<T> target) {
+		isNotNull();
+		T value = convertToTargetType(target);
+		return Assertions.assertThat(value);
+	}
+
+	/**
+	 * Verify that the actual value can be converted to an instance of the type
+	 * defined by the given {@link AssertFactory} and return a new Assert narrowed
+	 * to that type.
+	 * <p>{@link InstanceOfAssertFactories} provides static factories for all the
+	 * types supported by {@link Assertions#assertThat}. Additional factories can
+	 * be created by implementing {@link AssertFactory}.
+	 * <p>Example: <pre><code class="java">
+	 * // Check that the JSON document is an array of 3 users
+	 * assertThat(json).convertTo(InstanceOfAssertFactories.list(User.class))
+	 *         hasSize(3); // ListAssert of User
+	 * </code></pre>
+	 * @param assertFactory the {@link AssertFactory} to use to produce a narrowed
+	 * Assert for the type that it defines.
+	 */
+	public <ASSERT extends AbstractAssert<?, ?>> ASSERT convertTo(AssertFactory<?, ASSERT> assertFactory) {
+		isNotNull();
+		return assertFactory.createAssert(this::convertToTargetType);
+	}
+
+	@SuppressWarnings("unchecked")
+	private <T> T convertToTargetType(Type targetType) {
+		String json = this.actual.getJson();
+		if (this.jsonMessageConverter == null) {
+			throw new IllegalStateException(
+					"No JSON message converter available to convert %s".formatted(json));
+		}
+		try {
+			return (T) this.jsonMessageConverter.read(targetType, getClass(), fromJson(json));
+		}
+		catch (Exception ex) {
+			throw failure(new ValueProcessingFailed(json,
+					"To convert successfully to:%n  %s%nBut it failed:%n  %s%n".formatted(
+							targetType.getTypeName(), ex.getMessage())));
+		}
+	}
+
+	private HttpInputMessage fromJson(String json) {
+		MockHttpInputMessage inputMessage = new MockHttpInputMessage(json.getBytes(StandardCharsets.UTF_8));
+		inputMessage.getHeaders().add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE);
+		return inputMessage;
+	}
+
+
 	// JsonPath support
 
 	/**
@@ -525,4 +590,11 @@ private JsonPathNotExpected(String actual, String path) {
 		}
 	}
 
+	private static final class ValueProcessingFailed extends BasicErrorMessageFactory {
+
+		private ValueProcessingFailed(String actualToString, String errorMessage) {
+			super("%nExpected:%n  %s%n%s".formatted(actualToString, errorMessage));
+		}
+	}
+
 }

spring-test/src/test/java/org/springframework/test/json/AbstractJsonContentAssertTests.java

@@ -26,9 +26,12 @@
 import java.util.function.Consumer;
 import java.util.stream.Stream;
 
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import org.assertj.core.api.AbstractObjectAssert;
 import org.assertj.core.api.AssertProvider;
 import org.assertj.core.api.InstanceOfAssertFactories;
+import org.assertj.core.api.InstanceOfAssertFactory;
 import org.json.JSONException;
 import org.json.JSONObject;
 import org.junit.jupiter.api.Nested;
@@ -100,6 +103,56 @@ void satisfiesAllowFurtherAssertions() {
 		});
 	}
 
+	@Nested
+	class ConversionTests {
+
+		@Test
+		void convertToTargetType() {
+			assertThat(forJson(SIMPSONS, jsonHttpMessageConverter))
+					.convertTo(Family.class)
+					.satisfies(family -> assertThat(family.familyMembers()).hasSize(5));
+		}
+
+		@Test
+		void convertToIncompatibleTargetTypeShouldFail() {
+			AbstractJsonContentAssert<?> jsonAssert = assertThat(forJson(SIMPSONS, jsonHttpMessageConverter));
+			assertThatExceptionOfType(AssertionError.class)
+					.isThrownBy(() -> jsonAssert.convertTo(Member.class))
+					.withMessageContainingAll("To convert successfully to:",
+							Member.class.getName(), "But it failed:");
+		}
+
+		@Test
+		void convertUsingAssertFactory() {
+			assertThat(forJson(SIMPSONS, jsonHttpMessageConverter))
+					.convertTo(new FamilyAssertFactory())
+					.hasFamilyMember("Homer");
+		}
+
+		private AssertProvider<AbstractJsonContentAssert<?>> forJson(@Nullable String json,
+				@Nullable GenericHttpMessageConverter<Object> jsonHttpMessageConverter) {
+
+			return () -> new TestJsonContentAssert(json, jsonHttpMessageConverter);
+		}
+
+		private static class FamilyAssertFactory extends InstanceOfAssertFactory<Family, FamilyAssert> {
+			public FamilyAssertFactory() {
+				super(Family.class, FamilyAssert::new);
+			}
+		}
+
+		private static class FamilyAssert extends AbstractObjectAssert<FamilyAssert, Family> {
+			public FamilyAssert(Family family) {
+				super(family, FamilyAssert.class);
+			}
+
+			public FamilyAssert hasFamilyMember(String name) {
+				assertThat(this.actual.familyMembers).anySatisfy(m -> assertThat(m.name()).isEqualTo(name));
+				return this.myself;
+			}
+		}
+	}
+
 	@Nested
 	class HasPathTests {
 
@@ -261,14 +314,14 @@ void asMapIsEmpty() {
 		void convertToWithoutHttpMessageConverterShouldFail() {
 			JsonPathValueAssert path = assertThat(forJson(SIMPSONS)).extractingPath("$.familyMembers[0]");
 			assertThatIllegalStateException()
-					.isThrownBy(() -> path.convertTo(ExtractingPathTests.Member.class))
+					.isThrownBy(() -> path.convertTo(Member.class))
 					.withMessage("No JSON message converter available to convert {name=Homer}");
 		}
 
 		@Test
 		void convertToTargetType() {
 			assertThat(forJson(SIMPSONS, jsonHttpMessageConverter))
-					.extractingPath("$.familyMembers[0]").convertTo(ExtractingPathTests.Member.class)
+					.extractingPath("$.familyMembers[0]").convertTo(Member.class)
 					.satisfies(member -> assertThat(member.name).isEqualTo("Homer"));
 		}
 
@@ -283,7 +336,7 @@ void convertToIncompatibleTargetTypeShouldFail() {
 		}
 
 		@Test
-		void convertArrayToParameterizedType() {
+		void convertArrayUsingAssertFactory() {
 			assertThat(forJson(SIMPSONS, jsonHttpMessageConverter))
 					.extractingPath("$.familyMembers")
 					.convertTo(InstanceOfAssertFactories.list(Member.class))
@@ -336,8 +389,6 @@ void isNotEmptyForPathWithFilterNotMatching() {
 		}
 
 
-		private record Member(String name) {}
-
 		private record Customer(long id, String username) {}
 
 		private AssertProvider<AbstractJsonContentAssert<?>> forJson(@Nullable String json) {
@@ -836,6 +887,12 @@ private AssertProvider<AbstractJsonContentAssert<?>> forJson(@Nullable String js
 		return () -> new TestJsonContentAssert(json, null);
 	}
 
+
+	record Member(String name) {}
+
+	@JsonIgnoreProperties(ignoreUnknown = true)
+	record Family(List<Member> familyMembers) {}
+
 	private static class TestJsonContentAssert extends AbstractJsonContentAssert<TestJsonContentAssert> {
 
 		public TestJsonContentAssert(@Nullable String json, @Nullable GenericHttpMessageConverter<Object> jsonMessageConverter) {