8. Contract DSL

You can add a description to your contract. The description is arbitrary text. The following code shows an example:

Groovy DSL. 

		org.springframework.cloud.contract.spec.Contract.make {
			description('''
given:
	An input
when:
	Sth happens
then:
	Output
''')
		}

YAML. 

description: Some description
name: some name
priority: 8
ignored: true
request:
  url: /foo
  queryParameters:
    a: b
    b: c
  method: PUT
  headers:
    foo: bar
    fooReq: baz
  body:
    foo: bar
  matchers:
    body:
      - path: $.foo
        type: by_regex
        value: bar
    headers:
      - key: foo
        regex: bar
response:
  status: 200
  headers:
    foo2: bar
    foo3: foo33
    fooRes: baz
  body:
    foo2: bar
    foo3: baz
  matchers:
    body:
      - path: $.foo2
        type: by_regex
        value: bar
      - path: $.foo3
        type: by_command
        value: executeMe($it)
    headers:
      - key: foo2
        regex: bar
      - key: foo3
        command: andMeToo($it)

You can provide a name for your contract. Assume that you provided the following name: should register a user. If you do so, the name of the autogenerated test is validate_should_register_a_user. Also, the name of the stub in a WireMock stub is should_register_a_user.json.

	Important
	You must ensure that the name does not contain any characters that make the generated test not compile. Also, remember that, if you provide the same name for multiple contracts, your autogenerated tests fail to compile and your generated stubs override each other.

Groovy DSL. 

org.springframework.cloud.contract.spec.Contract.make {
	name("some_special_name")
}

YAML. 

name: some name

If you want to ignore a contract, you can either set a value of ignored contracts in the plugin configuration or set the ignored property on the contract itself:

Groovy DSL. 

org.springframework.cloud.contract.spec.Contract.make {
	ignored()
}

YAML. 

ignored: true

Starting with version 1.2.0, you can pass values from files. Assume that you have the following resources in our project.

└── src
    └── test
        └── resources
            └── contracts
                ├── readFromFile.groovy
                ├── request.json
                └── response.json

Further assume that your contract is as follows:

Groovy DSL. 

import org.springframework.cloud.contract.spec.Contract

Contract.make {
	request {
		method('PUT')
		headers {
			contentType(applicationJson())
		}
		body(file("request.json"))
		url("/1")
	}
	response {
		status 200
		body(file("response.json"))
		headers {
			contentType(textPlain())
		}
	}
}

YAML. 

request:
  method: GET
  url: /foo
  bodyFromFile: request.json
response:
  status: 200
  bodyFromFile: response.json

Further assume that the JSON files is as follows:

request.json

{ "status" : "REQUEST" }

response.json

{ "status" : "RESPONSE" }

When test or stub generation takes place, the contents of the file is passed to the body of a request or a response. The name of the file needs to be a file with location relative to the folder in which the contract lays.

The following methods can be called in the top-level closure of a contract definition. request and response are mandatory. priority is optional.

Groovy DSL. 

org.springframework.cloud.contract.spec.Contract.make {
	// Definition of HTTP request part of the contract
	// (this can be a valid request or invalid depending
	// on type of contract being specified).
	request {
		//...
	}

	// Definition of HTTP response part of the contract
	// (a service implementing this contract should respond
	// with following response after receiving request
	// specified in "request" part above).
	response {
		//...
	}

	// Contract priority, which can be used for overriding
	// contracts (1 is highest). Priority is optional.
	priority 1
}

YAML. 

priority: 8
request:
...
response:
...

	Important
	If you want to make your contract have a higher value of priority you need to pass a lower number to the priority tag / method. E.g. priority with value 5 has higher priority than priority with value 10.

	Important
	This section is valid only for Groovy DSL. Check out the Section 8.5.7, “Dynamic Properties in the Matchers Sections” section for YAML examples of a similar feature.

You can set the properties inside the body either with the value method or, if you use the Groovy map notation, with $(). The following example shows how to set dynamic properties with the value method:

value(consumer(...), producer(...))
value(c(...), p(...))
value(stub(...), test(...))
value(client(...), server(...))

The following example shows how to set dynamic properties with $():

$(consumer(...), producer(...))
$(c(...), p(...))
$(stub(...), test(...))
$(client(...), server(...))

Both approaches work equally well. stub and client methods are aliases over the consumer method. Subsequent sections take a closer look at what you can do with those values.

	Important
	This section is valid only for Groovy DSL. Check out the Section 8.5.7, “Dynamic Properties in the Matchers Sections” section for YAML examples of a similar feature.

You can use regular expressions to write your requests in Contract DSL. Doing so is particularly useful when you want to indicate that a given response should be provided for requests that follow a given pattern. Also, you can use regular expressions when you need to use patterns and not exact values both for your test and your server side tests.

The following example shows how to use regular expressions to write a request:

org.springframework.cloud.contract.spec.Contract.make {
	request {
		method('GET')
		url $(consumer(~/\/[0-9]{2}/), producer('/12'))
	}
	response {
		status 200
		body(
				id: $(anyNumber()),
				surname: $(
						consumer('Kowalsky'),
						producer(regex('[a-zA-Z]+'))
				),
				name: 'Jan',
				created: $(consumer('2014-02-02 12:23:43'), producer(execute('currentDate(it)'))),
				correlationId: value(consumer('5d1f9fef-e0dc-4f3d-a7e4-72d2220dd827'),
						producer(regex('[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12}'))
				)
		)
		headers {
			header 'Content-Type': 'text/plain'
		}
	}
}

You can also provide only one side of the communication with a regular expression. If you do so, then the contract engine automatically provides the generated string that matches the provided regular expression. The following code shows an example:

org.springframework.cloud.contract.spec.Contract.make {
	request {
		method 'PUT'
		url value(consumer(regex('/foo/[0-9]{5}')))
		body([
			requestElement: $(consumer(regex('[0-9]{5}')))
		])
		headers {
			header('header', $(consumer(regex('application\\/vnd\\.fraud\\.v1\\+json;.*'))))
		}
	}
	response {
		status 200
		body([
			responseElement: $(producer(regex('[0-9]{7}')))
		])
		headers {
			contentType("application/vnd.fraud.v1+json")
		}
	}
}

In the preceding example, the opposite side of the communication has the respective data generated for request and response.

Spring Cloud Contract comes with a series of predefined regular expressions that you can use in your contracts, as shown in the following example:

protected static final Pattern TRUE_OR_FALSE = Pattern.compile(/(true|false)/)
protected static final Pattern ONLY_ALPHA_UNICODE = Pattern.compile(/[\p{L}]*/)
protected static final Pattern NUMBER = Pattern.compile('-?(\\d*\\.\\d+|\\d+)')
protected static final Pattern IP_ADDRESS = Pattern.compile('([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])')
protected static final Pattern HOSTNAME_PATTERN = Pattern.compile('((http[s]?|ftp):/)/?([^:/\\s]+)(:[0-9]{1,5})?')
protected static final Pattern EMAIL = Pattern.compile('[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,6}')
protected static final Pattern URL = UrlHelper.URL
protected static final Pattern UUID = Pattern.compile('[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}')
protected static final Pattern ANY_DATE = Pattern.compile('(\\d\\d\\d\\d)-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])')
protected static final Pattern ANY_DATE_TIME = Pattern.compile('([0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])')
protected static final Pattern ANY_TIME = Pattern.compile('(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])')
protected static final Pattern NON_EMPTY = Pattern.compile(/[\S\s]+/)
protected static final Pattern NON_BLANK = Pattern.compile(/^\s*\S[\S\s]*/)
protected static final Pattern ISO8601_WITH_OFFSET = Pattern.compile(/([0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(\.\d{3})?(Z|[+-][01]\d:[0-5]\d)/)

protected static Pattern anyOf(String... values){
	return Pattern.compile(values.collect({"^$it\$"}).join("|"))
}

String onlyAlphaUnicode() {
	return ONLY_ALPHA_UNICODE.pattern()
}

String number() {
	return NUMBER.pattern()
}

String anyBoolean() {
	return TRUE_OR_FALSE.pattern()
}

String ipAddress() {
	return IP_ADDRESS.pattern()
}

String hostname() {
	return HOSTNAME_PATTERN.pattern()
}

String email() {
	return EMAIL.pattern()
}

String url() {
	return URL.pattern()
}

String uuid(){
	return UUID.pattern()
}

String isoDate() {
	return ANY_DATE.pattern()
}

String isoDateTime() {
	return ANY_DATE_TIME.pattern()
}

String isoTime() {
	return ANY_TIME.pattern()
}

String iso8601WithOffset() {
	return ISO8601_WITH_OFFSET.pattern()
}

String nonEmpty() {
	return NON_EMPTY.pattern()
}

String nonBlank() {
	return NON_BLANK.pattern()
}

In your contract, you can use it as shown in the following example:

Contract dslWithOptionalsInString = Contract.make {
	priority 1
	request {
		method POST()
		url '/users/password'
		headers {
			contentType(applicationJson())
		}
		body(
				email: $(consumer(optional(regex(email()))), producer('[email protected]')),
				callback_url: $(consumer(regex(hostname())), producer('https://partners.com'))
		)
	}
	response {
		status 404
		headers {
			contentType(applicationJson())
		}
		body(
				code: value(consumer("123123"), producer(optional("123123"))),
				message: "User not found by email = [${value(producer(regex(email())), consumer('[email protected]'))}]"
		)
	}
}

	Important
	This section is valid only for Groovy DSL. Check out the Section 8.5.7, “Dynamic Properties in the Matchers Sections” section for YAML examples of a similar feature.

It is possible to provide optional parameters in your contract. However, you can provide optional parameters only for the following:

The following example shows how to provide optional parameters:

org.springframework.cloud.contract.spec.Contract.make {
	priority 1
	request {
		method 'POST'
		url '/users/password'
		headers {
			contentType(applicationJson())
		}
		body(
				email: $(consumer(optional(regex(email()))), producer('[email protected]')),
				callback_url: $(consumer(regex(hostname())), producer('https://partners.com'))
		)
	}
	response {
		status 404
		headers {
			header 'Content-Type': 'application/json'
		}
		body(
				code: value(consumer("123123"), producer(optional("123123")))
		)
	}
}

By wrapping a part of the body with the optional() method, you create a regular expression that must be present 0 or more times.

If you use Spock for, the following test would be generated from the previous example:

"""
 given:
  def request = given()
    .header("Content-Type", "application/json")
    .body('''{"email":"[email protected]","callback_url":"https://partners.com"}''')

 when:
  def response = given().spec(request)
    .post("/users/password")

 then:
  response.statusCode == 404
  response.header('Content-Type')  == 'application/json'
 and:
  DocumentContext parsedJson = JsonPath.parse(response.body.asString())
  assertThatJson(parsedJson).field("['code']").matches("(123123)?")
"""

The following stub would also be generated:

'''
{
  "request" : {
	"url" : "/users/password",
	"method" : "POST",
	"bodyPatterns" : [ {
	  "matchesJsonPath" : "$[?(@.['email'] =~ /([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\\\.[a-zA-Z]{2,6})?/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.['callback_url'] =~ /((http[s]?|ftp):\\\\/)\\\\/?([^:\\\\/\\\\s]+)(:[0-9]{1,5})?/)]"
	} ],
	"headers" : {
	  "Content-Type" : {
		"equalTo" : "application/json"
	  }
	}
  },
  "response" : {
	"status" : 404,
	"body" : "{\\"code\\":\\"123123\\",\\"message\\":\\"User not found by email == [not.existing@user.com]\\"}",
	"headers" : {
	  "Content-Type" : "application/json"
	}
  },
  "priority" : 1
}
'''

	Important
	This section is valid only for Groovy DSL. Check out the Section 8.5.7, “Dynamic Properties in the Matchers Sections” section for YAML examples of a similar feature.

You can define a method call that executes on the server side during the test. Such a method can be added to the class defined as "baseClassForTests" in the configuration. The following code shows an example of the contract portion of the test case:

org.springframework.cloud.contract.spec.Contract.make {
	request {
		method 'PUT'
		url $(consumer(regex('^/api/[0-9]{2}$')), producer('/api/12'))
		headers {
			header 'Content-Type': 'application/json'
		}
		body '''\
				[{
					"text": "Gonna see you at Warsaw"
				}]
			'''
	}
	response {
		body (
				path: $(consumer('/api/12'), producer(regex('^/api/[0-9]{2}$'))),
				correlationId: $(consumer('1223456'), producer(execute('isProperCorrelationId($it)')))
		)
		status 200
	}
}

The following code shows the base class portion of the test case:

abstract class BaseMockMvcSpec extends Specification {

	def setup() {
		RestAssuredMockMvc.standaloneSetup(new PairIdController())
	}

	void isProperCorrelationId(Integer correlationId) {
		assert correlationId == 123456
	}

	void isEmpty(String value) {
		assert value == null
	}

}

	Important
	You cannot use both a String and execute to perform concatenation. For example, calling header('Authorization', 'Bearer ' + execute('authToken()')) leads to improper results. Instead, call header('Authorization', execute('authToken()')) and ensure that the authToken() method returns everything you need.

The type of the object read from the JSON can be one of the following, depending on the JSON path:

In the request part of the contract, you can specify that the body should be taken from a method.

	Important
	You must provide both the consumer and the producer side. The execute part is applied for the whole body - not for parts of it.

The following example shows how to read an object from JSON:

Contract contractDsl = Contract.make {
	request {
		method 'GET'
		url '/something'
		body(
				$(c("foo"), p(execute("hashCode()")))
		)
	}
	response {
		status 200
	}
}

The preceding example results in calling the hashCode() method in the request body. It should resemble the following code:

// given:
 MockMvcRequestSpecification request = given()
   .body(hashCode());

// when:
 ResponseOptions response = given().spec(request)
   .get("/something");

// then:
 assertThat(response.statusCode()).isEqualTo(200);

The best situation is to provide fixed values, but sometimes you need to reference a request in your response.

If you’re writing contracts using Groovy DSL, you can use the fromRequest() method, which lets you reference a bunch of elements from the HTTP request. You can use the following options:

If you’re using the YAML contract definition you have to use the Handlebars {{{ }}} notation with custom, Spring Cloud Contract functions to achieve this.

Consider the following contract:

Groovy DSL. 

Contract contractDsl = Contract.make {
	request {
		method 'GET'
		url('/api/v1/xxxx') {
			queryParameters {
				parameter("foo", "bar")
				parameter("foo", "bar2")
			}
		}
		headers {
			header(authorization(), "secret")
			header(authorization(), "secret2")
		}
		body(foo: "bar", baz: 5)
	}
	response {
		status 200
		headers {
			header(authorization(), "foo ${fromRequest().header(authorization())} bar")
		}
		body(
				url: fromRequest().url(),
				path: fromRequest().path(),
				pathIndex: fromRequest().path(1),
				param: fromRequest().query("foo"),
				paramIndex: fromRequest().query("foo", 1),
				authorization: fromRequest().header("Authorization"),
				authorization2: fromRequest().header("Authorization", 1),
				fullBody: fromRequest().body(),
				responseFoo: fromRequest().body('$.foo'),
				responseBaz: fromRequest().body('$.baz'),
				responseBaz2: "Bla bla ${fromRequest().body('$.foo')} bla bla"
		)
	}
}

YAML. 

request:
  method: GET
  url: /api/v1/xxxx
  queryParameters:
    foo:
      - bar
      - bar2
  headers:
    Authorization:
      - secret
      - secret2
  body:
    foo: bar
    baz: 5
response:
  status: 200
  headers:
    Authorization: "foo {{{ request.headers.Authorization.0 }}} bar"
  body:
    url: "{{{ request.url }}}"
    path: "{{{ request.path }}}"
    pathIndex: "{{{ request.path.1 }}}"
    param: "{{{ request.query.foo }}}"
    paramIndex: "{{{ request.query.foo.1 }}}"
    authorization: "{{{ request.headers.Authorization.0 }}}"
    authorization2: "{{{ request.headers.Authorization.1 }}"
    fullBody: "{{{ request.body }}}"
    responseFoo: "{{{ jsonpath this '$.foo' }}}"
    responseBaz: "{{{ jsonpath this '$.baz' }}}"
    responseBaz2: "Bla bla {{{ jsonpath this '$.foo' }}} bla bla"

Running a JUnit test generation leads to a test that resembles the following example:

// given:
 MockMvcRequestSpecification request = given()
   .header("Authorization", "secret")
   .header("Authorization", "secret2")
   .body("{\"foo\":\"bar\",\"baz\":5}");

// when:
 ResponseOptions response = given().spec(request)
   .queryParam("foo","bar")
   .queryParam("foo","bar2")
   .get("/api/v1/xxxx");

// then:
 assertThat(response.statusCode()).isEqualTo(200);
 assertThat(response.header("Authorization")).isEqualTo("foo secret bar");
// and:
 DocumentContext parsedJson = JsonPath.parse(response.getBody().asString());
 assertThatJson(parsedJson).field("['fullBody']").isEqualTo("{\"foo\":\"bar\",\"baz\":5}");
 assertThatJson(parsedJson).field("['authorization']").isEqualTo("secret");
 assertThatJson(parsedJson).field("['authorization2']").isEqualTo("secret2");
 assertThatJson(parsedJson).field("['path']").isEqualTo("/api/v1/xxxx");
 assertThatJson(parsedJson).field("['param']").isEqualTo("bar");
 assertThatJson(parsedJson).field("['paramIndex']").isEqualTo("bar2");
 assertThatJson(parsedJson).field("['pathIndex']").isEqualTo("v1");
 assertThatJson(parsedJson).field("['responseBaz']").isEqualTo(5);
 assertThatJson(parsedJson).field("['responseFoo']").isEqualTo("bar");
 assertThatJson(parsedJson).field("['url']").isEqualTo("/api/v1/xxxx?foo=bar&foo=bar2");
 assertThatJson(parsedJson).field("['responseBaz2']").isEqualTo("Bla bla bar bla bla");

As you can see, elements from the request have been properly referenced in the response.

The generated WireMock stub should resemble the following example:

{
  "request" : {
    "urlPath" : "/api/v1/xxxx",
    "method" : "POST",
    "headers" : {
      "Authorization" : {
        "equalTo" : "secret2"
      }
    },
    "queryParameters" : {
      "foo" : {
        "equalTo" : "bar2"
      }
    },
    "bodyPatterns" : [ {
      "matchesJsonPath" : "$[?(@.['baz'] == 5)]"
    }, {
      "matchesJsonPath" : "$[?(@.['foo'] == 'bar')]"
    } ]
  },
  "response" : {
    "status" : 200,
    "body" : "{\"authorization\":\"{{{request.headers.Authorization.[0]}}}\",\"path\":\"{{{request.path}}}\",\"responseBaz\":{{{jsonpath this '$.baz'}}} ,\"param\":\"{{{request.query.foo.[0]}}}\",\"pathIndex\":\"{{{request.path.[1]}}}\",\"responseBaz2\":\"Bla bla {{{jsonpath this '$.foo'}}} bla bla\",\"responseFoo\":\"{{{jsonpath this '$.foo'}}}\",\"authorization2\":\"{{{request.headers.Authorization.[1]}}}\",\"fullBody\":\"{{{escapejsonbody}}}\",\"url\":\"{{{request.url}}}\",\"paramIndex\":\"{{{request.query.foo.[1]}}}\"}",
    "headers" : {
      "Authorization" : "{{{request.headers.Authorization.[0]}}};foo"
    },
    "transformers" : [ "response-template" ]
  }
}

Sending a request such as the one presented in the request part of the contract results in sending the following response body:

{
  "url" : "/api/v1/xxxx?foo=bar&foo=bar2",
  "path" : "/api/v1/xxxx",
  "pathIndex" : "v1",
  "param" : "bar",
  "paramIndex" : "bar2",
  "authorization" : "secret",
  "authorization2" : "secret2",
  "fullBody" : "{\"foo\":\"bar\",\"baz\":5}",
  "responseFoo" : "bar",
  "responseBaz" : 5,
  "responseBaz2" : "Bla bla bar bla bla"
}

	Important
	This feature works only with WireMock having a version greater than or equal to 2.5.1. The Spring Cloud Contract Verifier uses WireMock’s response-template response transformer. It uses Handlebars to convert the Mustache {{{ }}} templates into proper values. Additionally, it registers two helper functions:

WireMock lets you register custom extensions. By default, Spring Cloud Contract registers the transformer, which lets you reference a request from a response. If you want to provide your own extensions, you can register an implementation of the org.springframework.cloud.contract.verifier.dsl.wiremock.WireMockExtensions interface. Since we use the spring.factories extension approach, you can create an entry in META-INF/spring.factories file similar to the following:

org.springframework.cloud.contract.verifier.dsl.wiremock.WireMockExtensions=\
org.springframework.cloud.contract.stubrunner.provider.wiremock.TestWireMockExtensions

The following is an example of a custom extension:

TestWireMockExtensions.groovy. 

package org.springframework.cloud.contract.verifier.dsl.wiremock

import com.github.tomakehurst.wiremock.extension.Extension

/**
 * Extension that registers the default transformer and the custom one
 */
class TestWireMockExtensions implements WireMockExtensions {
	@Override
	List<Extension> extensions() {
		return [
				new DefaultResponseTransformer(),
				new CustomExtension()
		]
	}
}

class CustomExtension implements Extension {

	@Override
	String getName() {
		return "foo-transformer"
	}
}

	Important
	Remember to override the applyGlobally() method and set it to false if you want the transformation to be applied only for a mapping that explicitly requires it.

If you work with Pact, the following discussion may seem familiar. Quite a few users are used to having a separation between the body and setting the dynamic parts of a contract.

You can use two separate sections:

Currently, Spring Cloud Contract Verifier supports only JSON Path-based matchers with the following matching possibilities:

YAML. Please read the Groovy section for detailed explanation of what the types mean

For YAML the structure of a matcher looks like this

- path: $.foo
  type: by_regex
  value: bar

Or if you want to use one of the predefined regular expressions [only_alpha_unicode, number, any_boolean, ip_address, hostname, email, url, uuid, iso_date, iso_date_time, iso_time, iso_8601_with_offset, non_empty, non_blank]:

- path: $.foo
  type: by_regex
  predefined: only_alpha_unicode

Below you can find the allowed list of `type`s.

Consider the following example:

Groovy DSL. 

Contract contractDsl = Contract.make {
	request {
		method 'GET'
		urlPath '/get'
		body([
				duck: 123,
				alpha: "abc",
				number: 123,
				aBoolean: true,
				date: "2017-01-01",
				dateTime: "2017-01-01T01:23:45",
				time: "01:02:34",
				valueWithoutAMatcher: "foo",
				valueWithTypeMatch: "string",
				key: [
						'complex.key' : 'foo'
				]
		])
		stubMatchers {
			jsonPath('$.duck', byRegex("[0-9]{3}"))
			jsonPath('$.duck', byEquality())
			jsonPath('$.alpha', byRegex(onlyAlphaUnicode()))
			jsonPath('$.alpha', byEquality())
			jsonPath('$.number', byRegex(number()))
			jsonPath('$.aBoolean', byRegex(anyBoolean()))
			jsonPath('$.date', byDate())
			jsonPath('$.dateTime', byTimestamp())
			jsonPath('$.time', byTime())
			jsonPath("\$.['key'].['complex.key']", byEquality())
		}
		headers {
			contentType(applicationJson())
		}
	}
	response {
		status 200
		body([
				duck: 123,
				alpha: "abc",
				number: 123,
				aBoolean: true,
				date: "2017-01-01",
				dateTime: "2017-01-01T01:23:45",
				time: "01:02:34",
				valueWithoutAMatcher: "foo",
				valueWithTypeMatch: "string",
				valueWithMin: [
					1,2,3
				],
				valueWithMax: [
					1,2,3
				],
				valueWithMinMax: [
					1,2,3
				],
				valueWithMinEmpty: [],
				valueWithMaxEmpty: [],
				key: [
				        'complex.key' : 'foo'
				]
		])
		testMatchers {
			// asserts the jsonpath value against manual regex
			jsonPath('$.duck', byRegex("[0-9]{3}"))
			// asserts the jsonpath value against the provided value
			jsonPath('$.duck', byEquality())
			// asserts the jsonpath value against some default regex
			jsonPath('$.alpha', byRegex(onlyAlphaUnicode()))
			jsonPath('$.alpha', byEquality())
			jsonPath('$.number', byRegex(number()))
			jsonPath('$.aBoolean', byRegex(anyBoolean()))
			// asserts vs inbuilt time related regex
			jsonPath('$.date', byDate())
			jsonPath('$.dateTime', byTimestamp())
			jsonPath('$.time', byTime())
			// asserts that the resulting type is the same as in response body
			jsonPath('$.valueWithTypeMatch', byType())
			jsonPath('$.valueWithMin', byType {
				// results in verification of size of array (min 1)
				minOccurrence(1)
			})
			jsonPath('$.valueWithMax', byType {
				// results in verification of size of array (max 3)
				maxOccurrence(3)
			})
			jsonPath('$.valueWithMinMax', byType {
				// results in verification of size of array (min 1 & max 3)
				minOccurrence(1)
				maxOccurrence(3)
			})
			jsonPath('$.valueWithMinEmpty', byType {
				// results in verification of size of array (min 0)
				minOccurrence(0)
			})
			jsonPath('$.valueWithMaxEmpty', byType {
				// results in verification of size of array (max 0)
				maxOccurrence(0)
			})
			// will execute a method `assertThatValueIsANumber`
			jsonPath('$.duck', byCommand('assertThatValueIsANumber($it)'))
			jsonPath("\$.['key'].['complex.key']", byEquality())
		}
		headers {
			contentType(applicationJson())
		}
	}
}

YAML. 

request:
  method: GET
  urlPath: /get
  body:
    duck: 123
    alpha: "abc"
    number: 123
    aBoolean: true
    date: "2017-01-01"
    dateTime: "2017-01-01T01:23:45"
    time: "01:02:34"
    valueWithoutAMatcher: "foo"
    valueWithTypeMatch: "string"
    key:
      "complex.key": 'foo'
  matchers:
    headers:
      - key: Content-Type
        regex: "application/json.*"
    body:
      - path: $.duck
        type: by_regex
        value: "[0-9]{3}"
      - path: $.duck
        type: by_equality
      - path: $.alpha
        type: by_regex
        predefined: only_alpha_unicode
      - path: $.alpha
        type: by_equality
      - path: $.number
        type: by_regex
        predefined: number
      - path: $.aBoolean
        type: by_regex
        predefined: any_boolean
      - path: $.date
        type: by_date
      - path: $.dateTime
        type: by_timestamp
      - path: $.time
        type: by_time
      - path: "$.['key'].['complex.key']"
        type: by_equality
  headers:
    Content-Type: application/json
response:
  status: 200
  body:
    duck: 123
    alpha: "abc"
    number: 123
    aBoolean: true
    date: "2017-01-01"
    dateTime: "2017-01-01T01:23:45"
    time: "01:02:34"
    valueWithoutAMatcher: "foo"
    valueWithTypeMatch: "string"
    valueWithMin:
      - 1
      - 2
      - 3
    valueWithMax:
      - 1
      - 2
      - 3
    valueWithMinMax:
      - 1
      - 2
      - 3
    valueWithMinEmpty: []
    valueWithMaxEmpty: []
    key:
      'complex.key' : 'foo'
  matchers:
    headers:
      - key: Content-Type
        regex: "application/json.*"
    body:
      - path: $.duck
        type: by_regex
        value: "[0-9]{3}"
      - path: $.duck
        type: by_equality
      - path: $.alpha
        type: by_regex
        predefined: only_alpha_unicode
      - path: $.alpha
        type: by_equality
      - path: $.number
        type: by_regex
        predefined: number
      - path: $.aBoolean
        type: by_regex
        predefined: any_boolean
      - path: $.date
        type: by_date
      - path: $.dateTime
        type: by_timestamp
      - path: $.time
        type: by_time
      - path: $.valueWithTypeMatch
        type: by_type
      - path: $.valueWithMin
        type: by_type
        minOccurrence: 1
      - path: $.valueWithMax
        type: by_type
        maxOccurrence: 3
      - path: $.valueWithMinMax
        type: by_type
        minOccurrence: 1
        maxOccurrence: 3
      - path: $.valueWithMinEmpty
        type: by_type
        minOccurrence: 0
      - path: $.valueWithMaxEmpty
        type: by_type
        maxOccurrence: 0
      - path: $.duck
        type: by_command
        value: assertThatValueIsANumber($it)
  headers:
    Content-Type: application/json

In the preceding example, you can see the dynamic portions of the contract in the matchers sections. For the request part, you can see that, for all fields but valueWithoutAMatcher, the values of the regular expressions that the stub should contain are explicitly set. For the valueWithoutAMatcher, the verification takes place in the same way as without the use of matchers. In that case, the test performs an equality check.

For the response side in the testMatchers section, we define the dynamic parts in a similar manner. The only difference is that the byType matchers are also present. The verifier engine checks four fields to verify whether the response from the test has a value for which the JSON path matches the given field, is of the same type as the one defined in the response body, and passes the following check (based on the method being called):

The resulting test would resemble the following example (note that an and section separates the autogenerated assertions and the assertion from matchers):

// given:
 MockMvcRequestSpecification request = given()
   .header("Content-Type", "application/json")
   .body("{\"duck\":123,\"alpha\":\"abc\",\"number\":123,\"aBoolean\":true,\"date\":\"2017-01-01\",\"dateTime\":\"2017-01-01T01:23:45\",\"time\":\"01:02:34\",\"valueWithoutAMatcher\":\"foo\",\"valueWithTypeMatch\":\"string\"}");

// when:
 ResponseOptions response = given().spec(request)
   .get("/get");

// then:
 assertThat(response.statusCode()).isEqualTo(200);
 assertThat(response.header("Content-Type")).matches("application/json.*");
// and:
 DocumentContext parsedJson = JsonPath.parse(response.getBody().asString());
 assertThatJson(parsedJson).field("valueWithoutAMatcher").isEqualTo("foo");
// and:
 assertThat(parsedJson.read("$.duck", String.class)).matches("[0-9]{3}");
 assertThat(parsedJson.read("$.duck", Integer.class)).isEqualTo(123);
 assertThat(parsedJson.read("$.alpha", String.class)).matches("[\\p{L}]*");
 assertThat(parsedJson.read("$.alpha", String.class)).isEqualTo("abc");
 assertThat(parsedJson.read("$.number", String.class)).matches("-?\\d*(\\.\\d+)?");
 assertThat(parsedJson.read("$.aBoolean", String.class)).matches("(true|false)");
 assertThat(parsedJson.read("$.date", String.class)).matches("(\\d\\d\\d\\d)-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])");
 assertThat(parsedJson.read("$.dateTime", String.class)).matches("([0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])");
 assertThat(parsedJson.read("$.time", String.class)).matches("(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])");
 assertThat((Object) parsedJson.read("$.valueWithTypeMatch")).isInstanceOf(java.lang.String.class);
 assertThat((Object) parsedJson.read("$.valueWithMin")).isInstanceOf(java.util.List.class);
 assertThat((java.lang.Iterable) parsedJson.read("$.valueWithMin", java.util.Collection.class)).hasSizeGreaterThanOrEqualTo(1);
 assertThat((Object) parsedJson.read("$.valueWithMax")).isInstanceOf(java.util.List.class);
 assertThat((java.lang.Iterable) parsedJson.read("$.valueWithMax", java.util.Collection.class)).hasSizeLessThanOrEqualTo(3);
 assertThat((Object) parsedJson.read("$.valueWithMinMax")).isInstanceOf(java.util.List.class);
 assertThat((java.lang.Iterable) parsedJson.read("$.valueWithMinMax", java.util.Collection.class)).hasSizeBetween(1, 3);
 assertThat((Object) parsedJson.read("$.valueWithMinEmpty")).isInstanceOf(java.util.List.class);
 assertThat((java.lang.Iterable) parsedJson.read("$.valueWithMinEmpty", java.util.Collection.class)).hasSizeGreaterThanOrEqualTo(0);
 assertThat((Object) parsedJson.read("$.valueWithMaxEmpty")).isInstanceOf(java.util.List.class);
 assertThat((java.lang.Iterable) parsedJson.read("$.valueWithMaxEmpty", java.util.Collection.class)).hasSizeLessThanOrEqualTo(0);
 assertThatValueIsANumber(parsedJson.read("$.duck"));

	Important
	Notice that, for the byCommand method, the example calls the assertThatValueIsANumber. This method must be defined in the test base class or be statically imported to your tests. Notice that the byCommand call was converted to assertThatValueIsANumber(parsedJson.read("$.duck"));. That means that the engine took the method name and passed the proper JSON path as a parameter to it.

The resulting WireMock stub is in the following example:

				'''
{
  "request" : {
	"urlPath" : "/get",
	"method" : "POST",
	"headers" : {
	  "Content-Type" : {
		"matches" : "application/json.*"
	  }
	},
	"bodyPatterns" : [ {
	  "matchesJsonPath" : "$[?(@.['valueWithoutAMatcher'] == 'foo')]"
	}, {
	  "matchesJsonPath" : "$[?(@.['valueWithTypeMatch'] == 'string')]"
	}, {
	  "matchesJsonPath" : "$.['list'].['some'].['nested'][?(@.['anothervalue'] == 4)]"
	}, {
	  "matchesJsonPath" : "$.['list'].['someother'].['nested'][?(@.['anothervalue'] == 4)]"
	}, {
	  "matchesJsonPath" : "$.['list'].['someother'].['nested'][?(@.['json'] == 'with value')]"
	}, {
	  "matchesJsonPath" : "$[?(@.duck =~ /([0-9]{3})/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.duck == 123)]"
	}, {
	  "matchesJsonPath" : "$[?(@.alpha =~ /([\\\\p{L}]*)/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.alpha == 'abc')]"
	}, {
	  "matchesJsonPath" : "$[?(@.number =~ /(-?(\\\\d*\\\\.\\\\d+|\\\\d+))/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.aBoolean =~ /((true|false))/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.date =~ /((\\\\d\\\\d\\\\d\\\\d)-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01]))/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.dateTime =~ /(([0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9]))/)]"
	}, {
	  "matchesJsonPath" : "$[?(@.time =~ /((2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9]))/)]"
	}, {
	  "matchesJsonPath" : "$.list.some.nested[?(@.json =~ /(.*)/)]"
	} ]
  },
  "response" : {
	"status" : 200,
	"body" : "{\\"date\\":\\"2017-01-01\\",\\"dateTime\\":\\"2017-01-01T01:23:45\\",\\"number\\":123,\\"aBoolean\\":true,\\"duck\\":123,\\"alpha\\":\\"abc\\",\\"valueWithMin\\":[1,2,3],\\"time\\":\\"01:02:34\\",\\"valueWithTypeMatch\\":\\"string\\",\\"valueWithMax\\":[1,2,3],\\"valueWithMinMax\\":[1,2,3],\\"valueWithoutAMatcher\\":\\"foo\\"}",
	"headers" : {
	  "Content-Type" : "application/json"
	}
  }
}
'''

	Important
	If you use a matcher, then the part of the request aned response that the matcher addresses with the JSON Path gets removed from the assertion. In the case of verifying a collection, you must create matchers for all the elements of the collection.

Consider the following example:

Contract.make {
    request {
        method 'GET'
        url("/foo")
    }
    response {
        status 200
        body(events: [[
                                 operation          : 'EXPORT',
                                 eventId            : '16f1ed75-0bcc-4f0d-a04d-3121798faf99',
                                 status             : 'OK'
                         ], [
                                 operation          : 'INPUT_PROCESSING',
                                 eventId            : '3bb4ac82-6652-462f-b6d1-75e424a0024a',
                                 status             : 'OK'
                         ]
                ]
        )
        testMatchers {
            jsonPath('$.events[0].operation', byRegex('.+'))
            jsonPath('$.events[0].eventId', byRegex('^([a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12})$'))
            jsonPath('$.events[0].status', byRegex('.+'))
        }
    }
}

The preceding code leads to creating the following test (the code block shows only the assertion section):

and:
	DocumentContext parsedJson = JsonPath.parse(response.body.asString())
	assertThatJson(parsedJson).array("['events']").contains("['eventId']").isEqualTo("16f1ed75-0bcc-4f0d-a04d-3121798faf99")
	assertThatJson(parsedJson).array("['events']").contains("['operation']").isEqualTo("EXPORT")
	assertThatJson(parsedJson).array("['events']").contains("['operation']").isEqualTo("INPUT_PROCESSING")
	assertThatJson(parsedJson).array("['events']").contains("['eventId']").isEqualTo("3bb4ac82-6652-462f-b6d1-75e424a0024a")
	assertThatJson(parsedJson).array("['events']").contains("['status']").isEqualTo("OK")
and:
	assertThat(parsedJson.read("\$.events[0].operation", String.class)).matches(".+")
	assertThat(parsedJson.read("\$.events[0].eventId", String.class)).matches("^([a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12})\$")
	assertThat(parsedJson.read("\$.events[0].status", String.class)).matches(".+")

As you can see, the assertion is malformed. Only the first element of the array got asserted. In order to fix this, you should apply the assertion to the whole $.events collection and assert it with the byCommand(…​) method.

The output message can be triggered by calling a method (such as a Scheduler when a was started and a message was sent), as shown in the following example:

Groovy DSL. 

def dsl = Contract.make {
	// Human readable description
	description 'Some description'
	// Label by means of which the output message can be triggered
	label 'some_label'
	// input to the contract
	input {
		// the contract will be triggered by a method
		triggeredBy('bookReturnedTriggered()')
	}
	// output message of the contract
	outputMessage {
		// destination to which the output message will be sent
		sentTo('output')
		// the body of the output message
		body('''{ "bookName" : "foo" }''')
		// the headers of the output message
		headers {
			header('BOOK-NAME', 'foo')
		}
	}
}

YAML. 

# Human readable description
description: Some description
# Label by means of which the output message can be triggered
label: some_label
input:
  # the contract will be triggered by a method
  triggeredBy: bookReturnedTriggered()
# output message of the contract
outputMessage:
  # destination to which the output message will be sent
  sentTo: output
  # the body of the output message
  body:
    bookName: foo
  # the headers of the output message
  headers:
    BOOK-NAME: foo

In the previous example case, the output message is sent to output if a method called bookReturnedTriggered is executed. On the message publisher’s side, we generate a test that calls that method to trigger the message. On the consumer side, you can use the some_label to trigger the message.

The output message can be triggered by receiving a message, as shown in the following example:

Groovy DSL. 

def dsl = Contract.make {
	description 'Some Description'
	label 'some_label'
	// input is a message
	input {
		// the message was received from this destination
		messageFrom('input')
		// has the following body
		messageBody([
		        bookName: 'foo'
		])
		// and the following headers
		messageHeaders {
			header('sample', 'header')
		}
	}
	outputMessage {
		sentTo('output')
		body([
		        bookName: 'foo'
		])
		headers {
			header('BOOK-NAME', 'foo')
		}
	}
}

YAML. 

# Human readable description
description: Some description
# Label by means of which the output message can be triggered
label: some_label
# input is a message
input:
  messageFrom: input
  # has the following body
  messageBody:
    bookName: 'foo'
  # and the following headers
  messageHeaders:
    sample: 'header'
# output message of the contract
outputMessage:
  # destination to which the output message will be sent
  sentTo: output
  # the body of the output message
  body:
    bookName: foo
  # the headers of the output message
  headers:
    BOOK-NAME: foo

In the preceding example, the output message is sent to output if a proper message is received on the input destination. On the message publisher’s side, the engine generates a test that sends the input message to the defined destination. On the consumer side, you can either send a message to the input destination or use a label (some_label in the example) to trigger the message.

	Important
	This section is valid only for Groovy DSL.

In HTTP, you have a notion of client/stub and `server/test notation. You can also use those paradigms in messaging. In addition, Spring Cloud Contract Verifier also provides the consumer and producer methods, as presented in the following example (note that you can use either $ or value methods to provide consumer and producer parts):

Contract.make {
	label 'some_label'
	input {
		messageFrom value(consumer('jms:output'), producer('jms:input'))
		messageBody([
				bookName: 'foo'
		])
		messageHeaders {
			header('sample', 'header')
		}
	}
	outputMessage {
		sentTo $(consumer('jms:input'), producer('jms:output'))
		body([
				bookName: 'foo'
		])
	}
}

In the input or outputMessage section you can call assertThat with the name of a method (e.g. assertThatMessageIsOnTheQueue()) that you have defined in the base class or in a static import. Spring Cloud Contract will execute that method in the generated test.