Adds handling for empty list and empty map response body (#1556)

Fixes gh-1423

spring-cloud-contract-verifier/src/main/groovy/org/springframework/cloud/contract/verifier/builder/JsonBodyVerificationBuilder.java

@@ -17,6 +17,7 @@
 package org.springframework.cloud.contract.verifier.builder;
 
 import java.math.BigDecimal;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Function;
@@ -102,6 +103,12 @@ class JsonBodyVerificationBuilder implements BodyMethodGeneration, ClassVerifier
 		Object copiedBody = cloneBody(convertedResponseBody);
 		convertedResponseBody = JsonToJsonPathsConverter
 				.removeMatchingJsonPaths(convertedResponseBody, bodyMatchers);
+
+		// If it was a map or list where all elements covered by matchers - json paths
+		// should not include empty check
+		boolean includeEmptyCheck = !mapOrListBodyReducedToEmpty(copiedBody,
+				convertedResponseBody);
+
 		// remove quotes from fromRequest objects before picking json paths
 		TestSideRequestTemplateModel templateModel = hasRequestBody()
 				? TestSideRequestTemplateModel.from(contract.getRequest()) : null;
@@ -109,7 +116,8 @@ class JsonBodyVerificationBuilder implements BodyMethodGeneration, ClassVerifier
 				returnReferencedEntries(templateModel), parsingClosure);
 		JsonPaths jsonPaths = new JsonToJsonPathsConverter(assertJsonSize)
 				.transformToJsonPathWithTestsSideValues(convertedResponseBody,
-						parsingClosure);
+						parsingClosure, includeEmptyCheck);
+
 		DocumentContext finalParsedRequestBody = parsedRequestBody;
 		jsonPaths.forEach(it -> {
 			String method = it.method();
@@ -123,6 +131,20 @@ class JsonBodyVerificationBuilder implements BodyMethodGeneration, ClassVerifier
 		return convertedResponseBody;
 	}
 
+	private boolean mapOrListBodyReducedToEmpty(Object originalBody,
+			Object convertedBody) {
+		int origSize = originalBody instanceof Map ? ((Map) originalBody).size() : -1;
+		int convertedSize = convertedBody instanceof Map ? ((Map) convertedBody).size()
+				: -1;
+		if (origSize > 0 && convertedSize == 0) {
+			return true;
+		}
+		origSize = originalBody instanceof List ? ((List) originalBody).size() : -1;
+		convertedSize = convertedBody instanceof List ? ((List) convertedBody).size()
+				: -1;
+		return (origSize > 0 && convertedSize == 0);
+	}
+
 	private boolean hasRequestBody() {
 		return contract.getRequest() != null && contract.getRequest().getBody() != null;
 	}

spring-cloud-contract-verifier/src/main/groovy/org/springframework/cloud/contract/verifier/util/JsonToJsonPathsConverter.groovy

@@ -320,13 +320,15 @@ class JsonToJsonPathsConverter {
 	}
 
 	JsonPaths transformToJsonPathWithTestsSideValues(def json,
-			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE) {
-		return transformToJsonPathWithValues(json, SERVER_SIDE, parsingClosure)
+			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE,
+			boolean includeEmptyCheck = false) {
+		return transformToJsonPathWithValues(json, SERVER_SIDE, parsingClosure, includeEmptyCheck)
 	}
 
 	JsonPaths transformToJsonPathWithStubsSideValues(def json,
-			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE) {
-		return transformToJsonPathWithValues(json, CLIENT_SIDE, parsingClosure)
+			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE,
+			boolean includeEmptyCheck = false) {
+		return transformToJsonPathWithValues(json, CLIENT_SIDE, parsingClosure, includeEmptyCheck)
 	}
 
 	static JsonPaths transformToJsonPathWithStubsSideValuesAndNoArraySizeCheck(def json,
@@ -336,11 +338,11 @@ class JsonToJsonPathsConverter {
 	}
 
 	private JsonPaths transformToJsonPathWithValues(def json, boolean clientSide,
-			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE) {
-		if (!json) {
+			Closure parsingClosure = MapConverter.JSON_PARSING_CLOSURE,
+			boolean includeEmptyCheck = false) {
+		if (json == null || (!json && !includeEmptyCheck)) {
 			return new JsonPaths()
 		}
-		JsonPaths pathsAndValues = [] as Set
 		Object convertedJson = MapConverter.
 				getClientOrServerSideValues(json, clientSide, parsingClosure)
 		Object jsonWithPatterns = ContentUtils.
@@ -349,6 +351,11 @@ class JsonToJsonPathsConverter {
 				new DelegatingJsonVerifiable(JsonAssertion.
 						assertThat(JsonOutput.toJson(jsonWithPatterns))
 														  .withoutThrowingException())
+		JsonPaths pathsAndValues = [] as Set
+		if (isRootElement(methodBufferingJsonPathVerifiable) && !json) {
+			pathsAndValues.add(methodBufferingJsonPathVerifiable.isEmpty())
+			return pathsAndValues
+		}
 		traverseRecursivelyForKey(jsonWithPatterns, methodBufferingJsonPathVerifiable,
 				{ MethodBufferingJsonVerifiable key, Object value ->
 					if (value instanceof ExecutionProperty || !(key instanceof FinishedDelegatingJsonVerifiable)) {

spring-cloud-contract-verifier/src/test/groovy/org/springframework/cloud/contract/verifier/builder/SpringTestMethodBodyBuildersSpec.groovy

@@ -578,6 +578,66 @@ class SpringTestMethodBodyBuildersSpec extends Specification implements WireMock
 			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
 	}
 
+	@Issue('#1423')
+	def 'should generate assertions for a response body containing an empty list with #methodBuilderName'() {
+		given:
+			Contract contractDsl = Contract.make {
+				request {
+					method "GET"
+					url "/url"
+				}
+				response {
+					status OK()
+					body("[]")
+				}
+			}
+			methodBuilder()
+		when:
+			String test = singleTestGenerator(contractDsl)
+		then:
+			test.contains("""assertThatJson(parsedJson).isEmpty()""")
+		and:
+			stubMappingIsValidWireMockStub(contractDsl)
+		and:
+			SyntaxChecker.tryToCompile(methodBuilderName, test)
+		where:
+			methodBuilderName | methodBuilder
+			"spock"           | { properties.testFramework = TestFramework.SPOCK }
+			"testng"          | { properties.testFramework = TestFramework.TESTNG }
+			"mockmvc"         | { properties.testMode = TestMode.MOCKMVC }
+			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
+	}
+
+	@Issue('#1423')
+	def 'should generate assertions for a response body containing an empty map with #methodBuilderName'() {
+		given:
+			Contract contractDsl = Contract.make {
+				request {
+					method "GET"
+					url "/url"
+				}
+				response {
+					status OK()
+					body("{}")
+				}
+			}
+			methodBuilder()
+		when:
+			String test = singleTestGenerator(contractDsl)
+		then:
+			test.contains("""assertThatJson(parsedJson).isEmpty()""")
+		and:
+			stubMappingIsValidWireMockStub(contractDsl)
+		and:
+			SyntaxChecker.tryToCompile(methodBuilderName, test)
+		where:
+			methodBuilderName | methodBuilder
+			"spock"           | { properties.testFramework = TestFramework.SPOCK }
+			"testng"          | { properties.testFramework = TestFramework.TESTNG }
+			"mockmvc"         | { properties.testMode = TestMode.MOCKMVC }
+			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
+	}
+
 	def 'should generate regex assertions for map objects in response body with #methodBuilderName'() {
 		given:
 			Contract contractDsl = Contract.make {

spring-cloud-contract-verifier/src/test/groovy/org/springframework/cloud/contract/verifier/builder/YamlMockMvcMethodBodyBuilderSpec.groovy

@@ -434,6 +434,68 @@ response:
 			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
 	}
 
+	@Issue('#1423')
+	def 'should generate assertions for a response body containing an empty list with #methodBuilderName'() {
+		given:
+			String contract = """\
+---
+description: Returns an empty collection
+request:
+  method: GET
+  urlPath: /url
+response:
+  status: 200
+  body: []
+"""
+			Contract contractDsl = fromYaml(contract)
+			methodBuilder()
+		when:
+			String test = singleTestGenerator(contractDsl)
+		then:
+			test.contains("""assertThatJson(parsedJson).isEmpty()""")
+		and:
+			stubMappingIsValidWireMockStub(contractDsl)
+		and:
+			SyntaxChecker.tryToCompile(methodBuilderName, test)
+		where:
+			methodBuilderName | methodBuilder
+			"spock"           | { properties.testFramework = TestFramework.SPOCK }
+			"testng"          | { properties.testFramework = TestFramework.TESTNG }
+			"mockmvc"         | { properties.testMode = TestMode.MOCKMVC }
+			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
+	}
+
+	@Issue('#1423')
+	def 'should generate assertions for a response body containing an empty map with #methodBuilderName'() {
+		given:
+			String contract = """\
+---
+description: Returns an empty map
+request:
+  method: GET
+  urlPath: /url
+response:
+  status: 200
+  body: {}
+"""
+			Contract contractDsl = fromYaml(contract)
+			methodBuilder()
+		when:
+			String test = singleTestGenerator(contractDsl)
+		then:
+			test.contains("""assertThatJson(parsedJson).isEmpty()""")
+		and:
+			stubMappingIsValidWireMockStub(contractDsl)
+		and:
+			SyntaxChecker.tryToCompile(methodBuilderName, test)
+		where:
+			methodBuilderName | methodBuilder
+			"spock"           | { properties.testFramework = TestFramework.SPOCK }
+			"testng"          | { properties.testFramework = TestFramework.TESTNG }
+			"mockmvc"         | { properties.testMode = TestMode.MOCKMVC }
+			"webclient"       | { properties.testMode = TestMode.WEBTESTCLIENT }
+	}
+
 	def 'should generate regex assertions for map objects in response body with #methodBuilderName'() {
 		given:
 			String contract = '''\