# CDC testing made simple with Pact
## What is Pact ?
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Pact is ***a contract testing tool***. Contract testing is a way to ensure that services (such as an API provider and a client) can communicate with each other. Without contract testing, the only way to know that services can communicate is by using expensive and brittle integration tests.
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Pact provides a testing button for your code, allowing you to safely confirm that your applications will work together without having to deploy the world first.
It is available on a lot of platforms and languages :
Pact comes with its own specification regarding the format of the contracts between consumers and providers :
## How can we implement a new service with Pact ?
Because we use a CDC approach we start with the consumer and here is what we want as a consumer :
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*As a consumer, I want a Rest API that returns “Hello world v1” when I GET “api/v1.0/helloworld”*
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### 1) Start with the consumer
Let’s implement a simple consumer by :
* Writing Test(s)
* Define interactions / Expectations
**Concretely** :
* Build your client : here we call it **consumer-js**
* Describe and configure the interactions (behaviors and expectations)
Once you have defined it you can run the tests. From those expectations Pact will create a contract file : a JSON file that will look like this :
### 2) Contract Driven Development
* Design Your **API** From The Contract
* Write a RED test
#### **The RED test (in .NET Core)**
The test will be launched and interactions will be verified based on the contract that has been defined on the consumer side.
#### **Make the test GREEN**
## Features offered by Pact
In this simple example we have just checked a GET interaction with simple string matcher but you can achieve much more complex and more realistic verifications with the tool :
## S.W\.O.T
Based on our experience with Pact here is our S.W\.O.T :
## Resources
Please find the code samples in this repository : [**https://github.com/agilepartner/pact-sandbox**](https://github.com/agilepartner/pact-sandbox)
To go further check the implementation guide in your favorite language :
## Conclusion
Pact is a really good tool to start a CDC approach. It is easy to use but there is one problem that needs to be solved before starting using it in enterprise :
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**Where the hell do we store the contracts ?**
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