Added the missing $() convenience method for messaging contracts (#623)

Fixes gh-619

(cherry picked from commit 4cf6e19)

spring-cloud-contract-spec/src/main/groovy/org/springframework/cloud/contract/spec/internal/Input.groovy

@@ -90,6 +90,10 @@ class Input extends Common {
 		return new DslProperty(client.clientValue, clientValue)
 	}
 
+	DslProperty $(ClientDslProperty client) {
+		return value(client)
+	}
+
 	@EqualsAndHashCode(includeFields = true, callSuper = true)
 	@ToString(includeSuper = true)
 	static class BodyType extends DslProperty {

spring-cloud-contract-spec/src/main/groovy/org/springframework/cloud/contract/spec/internal/OutputMessage.groovy

@@ -1,5 +1,5 @@
 /*
- *  Copyright 2013-2017 the original author or authors.
+ *  Copyright 2013-2018 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.
@@ -25,6 +25,14 @@ import repackaged.nl.flotsam.xeger.Xeger
 
 import java.util.regex.Pattern
 
+/**
+ * Represents an output for messaging. Used for verifying
+ * the body and headers that are sent.
+ *
+ * @author Marcin Grzejszczak
+ * @author Tim Ysewyn
+ * @since 1.0.0
+ */
 @TypeChecked
 @EqualsAndHashCode
 @ToString(includePackage = false, includeNames = true)
@@ -88,6 +96,10 @@ class OutputMessage extends Common {
 		return new DslProperty(value, server.serverValue)
 	}
 
+	DslProperty $(ServerDslProperty server) {
+		return value(server)
+	}
+
 	void testMatchers(@DelegatesTo(ResponseBodyMatchers) Closure closure) {
 		this.matchers = new ResponseBodyMatchers()
 		closure.delegate = this.matchers

spring-cloud-contract-spec/src/test/groovy/org/springframework/cloud/contract/spec/internal/InputSpec.groovy

@@ -0,0 +1,20 @@
+package org.springframework.cloud.contract.spec.internal
+
+import spock.lang.Specification
+/**
+ * @author Tim Ysewyn
+ */
+class InputSpec extends Specification {
+
+	def 'should set property when using the $() convenience method'() {
+		given:
+			Input input = new Input()
+			DslProperty property
+		when:
+			input.with {
+				property = $(consumer(regex("[0-9]{5}")))
+			}
+		then:
+			(property.serverValue as String).matches(/[0-9]{5}/)
+	}
+}

spring-cloud-contract-spec/src/test/groovy/org/springframework/cloud/contract/spec/internal/OutputMessageSpec.groovy

@@ -0,0 +1,20 @@
+package org.springframework.cloud.contract.spec.internal
+
+import spock.lang.Specification
+/**
+ * @author Tim Ysewyn
+ */
+class OutputMessageSpec extends Specification {
+
+	def 'should set property when using the $() convenience method'() {
+		given:
+			Input input = new Input()
+			DslProperty property
+		when:
+			input.with {
+				property = $(consumer(regex("[0-9]{5}")))
+			}
+		then:
+			(property.serverValue as String).matches(/[0-9]{5}/)
+	}
+}