How to verify stringified json in pact - json

Question

I am trying to build a pact between two services using asynchronous communication.
This is the code I used for generate the pact:
#ExtendWith(PactConsumerTestExt.class)
#PactTestFor(providerName = "provider", providerType = ProviderType.ASYNCH)
public class StringifiedPactTest {
#Pact(consumer = "consumer", provider = "provider")
public MessagePact generatePact(MessagePactBuilder builder) {
return builder.hasPactWith("provider")
.expectsToReceive("A valid aws sns event")
.withContent(new PactDslJsonBody().stringType(new String[]{"MessageId", "TopicArn"}).stringValue("Message", new PactDslJsonBody().stringType("Value", "Foo").toString()))
.toPact();
}
#Test
#PactTestFor(pactMethod = "generatePact")
public void buildPact(List<Message> messages) {
}
}
And the generated pact is
{
"consumer": {
"name": "consumer"
},
"provider": {
"name": "provider"
},
"messages": [
{
"description": "A valid aws sns event",
"metaData": {
"contentType": "application/json"
},
"contents": {
"TopicArn": "string",
"Message": "{\"Value\":\"Foo\"}",
"MessageId": "string"
},
"matchingRules": {
"body": {
"$.MessageId": {
"matchers": [
{
"match": "type"
}
],
"combine": "AND"
},
"$.TopicArn": {
"matchers": [
{
"match": "type"
}
],
"combine": "AND"
}
}
}
}
],
"metadata": {
"pactSpecification": {
"version": "3.0.0"
},
"pact-jvm": {
"version": "4.0.10"
}
}
}
This means the producer should have a "Message" that matches {"Value" : "Foo"}, any other combination like {"Value" : "Bar" } won't be successful.
Is there any way to add matching rules inside a stringified json?
Thanks!

Answer 1

Here's an anonymised example from a test we have. Hope it's useful. This creates a pact that matches only on type. So on the provider side, when I test against the contract, it doesn't matter what value I have for categoryName for example, as long as it's a stringType:
#PactTestFor(providerName = "provider-service", providerType = ProviderType.ASYNCH)
public class providerServiceConsumerPactTest {
private static String messageFromJson;
#BeforeAll
static void beforeAll() throws Exception {
messageFromJson = StreamUtils.copyToString(new ClassPathResource("/json/pact/consumer-service_provider-service.json").getInputStream(), Charset.defaultCharset());
}
#Pact(provider = "provider-service", consumer = "consumer-service")
public MessagePact providerServiceMessage(MessagePactBuilder builder) {
DslPart body = new PactDslJsonBody()
.object("metaData")
.stringType("origin", "provider-service")
.datetimeExpression("dateCreated", "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'")
.closeObject()
.minArrayLike("categories", 0, 1)
.stringType("id", "example data")
.stringType("categoryName", "example data")
.booleanType("clearance", false)
.closeObject()
.closeArray();
return builder
.expectsToReceive("a provider-service update")
.withContent(body)
.toPact();
}
#Test
#PactTestFor(pactMethod = "providerServiceMessage")
public void testProviderServiceMessage(MessagePact pact) {
// State
final String messageFromPact = pact.getMessages().get(0).contentsAsString();
// Assert
JSONAssert.assertEquals(messageFromPact, messageFromJson, false);
}

Answer 2

I'm having exactly the same issue, and unfortunately I don't think it's possible to tell Pact to parse the stringified JSON and look inside it (e.g. to verify that parse(Message).Value === "Foo" in your example).
The best you can do is write a regular expression to match the string you're expecting. This kind of sucks because there's no easy way to ignore the ordering of the JSON keys (e.g. "{\"a\":\"1\", \"b\":\"2\"}" and "{\"b\":\"2\", \"a\":\"1\"}" will compare different) but AFAIK Pact simply lacks the parsing functionality we're looking for, so the only tool it provides is regex.