Example of using contracts to perform integration testing in a pubsub microservices architecture.

echo-contract.json

[
  {
    "source": "consumer",
    "topic": "/echo",
    "payload": "echo"
  },
  {
    "source": "provider",
    "topic": "/echo",
    "payload": "echo"
  }
]

echo_consumer.js

// publish `message` to the "/echo" topic, and call `callback` on response
module.exports = function echo(connection, message, callback) {
  connection.subscribe('/echo', callback);
  connection.publish('/echo', message);
};

echo_consumer_test.js

var assert = require('assert');
var contracts = require('contracts'); // our home-built contract testing library
var echo = require('./echo_consumer');

// test the echo consumer
var stubConnection = contracts.connection();
echo(stubConnection, 'echo', function(response) {
  assert.equal(response, 'echo');  
});
stubConnection.testContract("echo-contract.json", { as: "consumer" });

echo_provider.go

package echo

type Connection interface {
  Subscribe(string, func(string))
  Publish(string, string)
}

// echo back any message sent to the "/echo" topic
func StartEchoProvider(connection Connection) {
  connection.Subscribe("/echo", func(message string) {
    connection.Publish("/echo", message)
  })
}

echo_provider_test.go

package echo

import (
  "testing"
  "contracts" // our home-built contract testing library
)

// test the echo provider
func TestEchoProvider(t *testing.T) {
  stubConnection := contracts.NewStubConnection()
  StartEchoProvider(stubConnection)
  stubConnection.TestContract(t, "echo-contract.json", contracts.asProvider)
}