Getting started

Setup

Specmatic can be used as a standalone executable and also included programmatically as part of your test suite.

For getting started quickly, let us use Specmatic standalone executable within our command line.

The Specmatic standalone executable is accessible through various prominent distribution channels.

  • Download the standalone jar from our Github releases or Maven Central.

    If you have downloaded the standalone jar from Maven Central, you may want to rename it as shown below for convenience.

    mv specmatic-executable-1.2.23-all.jar specmatic.jar
    

    Run specmatic as below to list all the options available

    java -jar specmatic.jar
    
  • Install specmatic npm package globally

    npm install -g specmatic
    

    Or you can run specmatic without installing it as below

    npx specmatic
    
  • Docker Pull Command for specmatic docker image

    docker pull znsio/specmatic
    

    Run specmatic by

    docker run znsio/specmatic
    

    Important: If you’re using a machine with an Apple Silicon chip, you’ll need to enable Rosetta for accelerated x86/amd64 binary emulation.

    Please follow these steps to do so:

    1. Update your Docker Desktop application to the latest version.
    2. Navigate to ‘Settings’, then ‘General Settings’.
    3. Ensure the Use Rosetta for x86/amd64 emulation on Apple Silicon option is checked.
    4. Save your settings and restart Docker Desktop for the changes to take effect.

Tip to run java jar easily

By following below tip running java -jar specmatic.jar every time can be avoided

  • Add this to the startup script of your shell like ~/.bashrc or ~/.zshrc

    alias specmatic='java -jar <path-to-jar>/specmatic.jar'
    

    Run specmatic by

    $ specmatic <options>
    
  • Create a batch file (specmatic.bat) with below content and add it your system path.

    java -jar <path-to-jar>/specmatic.jar %*
    

    The %* portion at the end tells the batch script to pass all of the parameters it receives to the new command.

    Run specmatic by

    C:\> specmatic.bat <options>
    

Example Application - PetStore

PetStore application has a backend API (Provider) and a front-end client application (Consumer). Here is a sequence diagram representing the getPetById operation.

UI (Consumer)          API (Provider)
      | --- getPetById ---> |
      | <-- {Pet JSON} ---- |

Before we get started, here is a quick refresher on the terminology used in the documentation.

  • Consumer - The application requesting the data (in this case UI)
  • Provider - The application responding with the data (in this case API)

PetStore API Specification

Below is the OpenAPI specification that represents the communication between UI and Backend in the above example application. Please save this to a file called service.yaml.

openapi: 3.0.1
info:
  title: Contract for the petstore service
  version: '1'
paths:
  /pets/{petid}:
    get:
      summary: Should be able to get a pet by petId
      parameters:
        - name: petid
          in: path
          required: true
          schema:
            type: number
          examples:
            SCOOBY_200_OK:
              value: 1
      responses:
        '200':
          description: Should be able to get a pet by petId
          content:
            application/json:
              schema:
                required:
                  - id
                  - name
                  - status
                  - type
                properties:
                  id:
                    type: number
                  name:
                    type: string
                  type:
                    type: string
                  status:
                    type: string
              examples:
                SCOOBY_200_OK:
                  value:
                    id: 1
                    name: Scooby
                    type: Golden Retriever
                    status: Adopted

Provider Side - Contract as a Test

We have a sample implementation of the PetStore API running which you can access through curl or any other tool of your choice.

curl https://my-json-server.typicode.com/znsio/specmatic-documentation/pets/1

Now lets use Specmatic to run the above API specification as a contract test against the Provider / API to see if it is adhering the OpenAPI Specification.

  • specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  • npx specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  •  docker run -v "/local-directory/service.yaml:/service.yaml" znsio/specmatic test "/service.yaml" --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    

Your output will look as shown in below (a few lines have been deleted in the interest of brevity).

API Specification Summary: service.yaml
  OpenAPI Version: 3.0.1
  API Paths: 1, API Operations: 1

Executing 1 tests

--------------------
  Request to https://my-json-server.typicode.com/znsio/specmatic-documentation at 2024-2-12 1:54:58.570
    GET /znsio/specmatic-documentation/pets/1
    

  Response at 2024-2-12 1:54:58.572
    200 OK
    Content-Type: application/json; charset=utf-8
    {
        "id": 1,
        "name": "Scooby",
        "type": "Golden Retriever",
        "status": "Adopted"
    }


Tests run: 1/1 (100%)

 Scenario: GET /pets/(petid:number) -> 200 | EX:SCOOBY_200_OK has SUCCEEDED

Could not load report configuration, coverage will be calculated but no coverage threshold will be enforced
|----------------------------------------------------------------------|
| API COVERAGE SUMMARY                                                 |
|----------------------------------------------------------------------|
| coverage | path          | method | response | # exercised | remarks |
|----------|---------------|--------|----------|-------------|---------|
|     100% | /pets/{petid} | GET    |      200 |           1 | covered |
|----------------------------------------------------------------------|
| 100% API Coverage reported from 1 path                               |
|----------------------------------------------------------------------|


Saving Open API Coverage Report json to ./build/reports/specmatic ...
Tests run: 1, Successes: 1, Failures: 0, Errors: 0

Understanding the output

  • Specmatic parsed your API specification and printed a brief API Specification Summary
  • Then it generated and started Executing 1 tests because our API specification contains only one endpoint with a single GET operation
  • Specmatic then logged the HTTP Request that it generated and the HTTP response it received from the API implementation
  • And finally it prints out the test results along with an API Coverage Report (Read our detailed post on API Converage Report to know more.)

Where did Specmatic get the test data to generate the HTTP request

How did Specmatic know to make the exact request to GET /znsio/specmatic-documentation/pets/1 with petId as “1”? And not just any other number?

In the OpenAPI spec you may have noticed that there is an examples section for petid with a named example called SCOOBY_200_OK.

  - name: "petid"
    in: "path"
    required: true
    schema:
      type: "number"
    examples:
      SCOOBY_200_OK:
        value: 1

Remove the examples section such that the petid param look as shown below.

  - name: "petid"
    in: "path"
    required: true
    schema:
      type: "number"

And try running the specmatic test command again.

  • specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  • npx specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  •  docker run -v "/local-directory/service.yaml:/service.yaml" znsio/specmatic test "/service.yaml" --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    

This will result in a test failure because the sample application returns a 404.

Unsuccessful Scenarios:
  " Scenario: GET /pets/(petid:number) -> 200 FAILED"
        Reason: Testing scenario "Should be able to get a pet by petId. Response: Should be able to get a pet by petId"
        API: GET /pets/(petid:number) -> 200
  
          >> RESPONSE.STATUS
          
             Expected status 200, actual was status 404

Tests run: 1, Successes: 0, Failures: 1, Errors: 0

This is because we removed the named example SCOOBY_200_OK, Specmatic generated a random petId based on the datatype of the petId path parameter. And since test data does not exist for this petId in the sample application, we get a 404.

--------------------
  Request to https://my-json-server.typicode.com/znsio/specmatic-documentation at 2024-2-11 5:44:5.791
    GET /znsio/specmatic-documentation/pets/318

Once you restore the OpenAPI file to its original state (add back the example petId value) the tests should start passing again.

How does this all work?

  • Specmatic is able to tie the named example SCOOBY_200_OK listed under the request parameters and the response sections of the OpenAPI spec to create a test.
  • This is also reflected in the name of the test where Specmatic displays the SCOOBY_200_OK in the test logs

Scenario: GET /pets/(petid:number) -> 200 | EX:SCOOBY_200_OK has SUCCEEDED

What happens when OpenAPI goes out of sync with the application or vice versa?

Now lets try something more interesting and change the datatype of the “status” field of response in OpenAPI file to “number” and save it.

  properties:
    status:
      type: "number"

Let us run the specmatic test command again.

  • specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  • npx specmatic test service.yaml --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    
  •  docker run -v "/local-directory/service.yaml:/service.yaml" znsio/specmatic test "/service.yaml" --testBaseURL=https://my-json-server.typicode.com/znsio/specmatic-documentation
    

This time around the test fails because the response from our sample app is not in line with the OpenAPI Specification.

Unsuccessful Scenarios:
  " Scenario: GET /pets/(petid:number) -> 200 | EX:SCOOBY_200_OK FAILED"
        Reason: Testing scenario "Should be able to get a pet by petId. Response: Should be able to get a pet by petId"
        API: GET /pets/(petid:number) -> 200
  
          >> RESPONSE.BODY.status
          
             Contract expected number but response contained "Adopted"

Tests run: 1, Successes: 0, Failures: 1, Errors: 0

This is how Specmatic is able to make sure that your API never deviates from the Specification.

Please refer to below videos for extensive demos on Contract as Test.

Learn more about Contract Tests here.

Consumer Side - Contract As A Stub / Intelligent Service Virtualisation

We have so far established that Specmatic will keep OpenAPI spec and the API implementation in sync. This gives us the confidence to use the same OpenAPI spec service.yaml on the Consumer side for Intelligent Service Virtualisation with Specmatic. This will help us isolate our UI development and make progress independent of the Provider / API. Here is a sequence diagram illustrating the same where UI no longer has to interact with the real backend for testing purposes. UI can instead rely on Specmatic Stub which is emulating the Provider / API.

UI (Consumer)         Specmatic Stub <- service.yaml
      | --- getPetById ---> |
      | <-- {Pet JSON} ---- |

Before we begin, please make sure that your service.yaml file is restored to its original state.

To spin up a stub server with the service.yaml we authored earlier, run below command.

  • specmatic stub service.yaml
    
  • npx specmatic stub service.yaml
    
  • docker run -v "/local-directory/service.yaml:/service.yaml" -p 9000:9000 znsio/specmatic stub "/service.yaml"
    

This should start your stub server on port 9000 by default as below.

Loading service.yaml
API Specification Summary: service.yaml
  OpenAPI Version: 3.0.1
  API Paths: 1, API Operations: 1


Stub server is running on http://0.0.0.0:9000. Ctrl + C to stop.

Tip: You can switch the port number by adding --port <port of your choice> in the command.

  • specmatic stub service.yaml --port 9002
    
  • npx specmatic stub service.yaml --port 9002
    
  • # Note that --port 9002 at the end of the command is crucial. It ensures that the stub 
    # server inside the Docker container is listening on the same port (9002) that's being
    # mapped to port 9000 on your machine. If these ports don't match, you won't be able to
    # access the stub server from your machine.
    docker run -v "/local-directory/service.yaml:/service.yaml" -p 9000:9002 znsio/specmatic stub "/service.yaml" --port 9002
    

Once the stub server is running you can verify the API by accessing it through Postman, Chrome, Curl etc.

curl http://localhost:9000/pets/123

You should now be able to see the response that matches the schema defined in your OpenAPI spec.

{
    "id": 864,
    "name": "VRIQA",
    "type": "KPNDQ",
    "status": 990
}

The response contains auto-generated values that adhere to the data type defined in the contract. In above output petid “864” is generated by specmatic and will vary with every execution.

However for petId 1, it will always return below values.

{
    "id": 1,
    "name": "Scooby",
    "type": "Golden Retriever",
    "status": "Adopted"
}

This is because the example SCOOBY_200_OK in the service.yaml spec file, which we earlier saw being used while running contract test, also serves a stub data when we run Specmatic stub.

With this we have effectively achived three goals in one go.

  • Examples serve as sample data for people referring to the API specification as documentation
  • The same examples are used in contract tests to create the HTTP request
  • And these examples also serve as stub data when we run Spemcatic stub command

Intelligent Service Virtualisation

Let us try a few experiments. Remove the status field in the 200_OKAY response example in service.yaml (the very last line in that file) and run the stub command again.

examples:
  200_OKAY:
    value:
      id: 1
      type: "Golden Retriever"
      name: "Scooby"
      status: "Adopted" # Remove this line

The stub server will auto reload your service.yaml file as soon as you save it. And you should see an output as shown below.

Loading service.yaml
API Specification Summary: service.yaml
  OpenAPI Version: 3.0.1
  API Paths: 1, API Operations: 1


[Example SCOOBY_200_OK]: Error from contract service.yaml

  In scenario "Should be able to get a pet by petId. Response: Should be able to get a pet by petId"
  API: GET /pets/(petid:number) -> 200
  
    >> RESPONSE.BODY.status
  
       key named status in the spec was not found in the "SCOOBY_200_OK" example

Specmatic rejects the expectation / canned response since it is not in line with the OpenAPI Specification.

Externalising stub responses

Please restore service.yaml to its original state(by adding back the status field in the SCOOBY_200_OK example) before proceeding with this section.

If you would like to add more stub responses, however you do not wish to bloat your specification with a lot of examples, we can also externalise the stub / canned responses to json files also.

  • Create a folder named service_data in the same folder as your service.yaml file (_data suffix is a naming convention that tell Specmatic to look for canned responses in that directory)
  • Create a json file with the name togo.json and add below contents to it
{
    "http-request": {
        "path": "/pets/2",
        "method": "GET"
    },
    "http-response": {
        "status": 200,
        "body": {
            "id": 2,
            "name": "Togo",
            "type": "Siberian Husky",
            "status": "Adopted"
        },
        "status-text": "OK"
    }
}

Now let us run the stub command again.

  • specmatic stub service.yaml
    
  • npx specmatic stub service.yaml
    
  • # Please note docker command here has to volume map the directory containing service.yaml 
    # to a directory within the container so that both service.yaml and folder service_data along 
    # with togo.json are available to Specmatic docker container
    docker run -v "/local-directory/:/specs" -p 9000:9000 znsio/specmatic stub "/specs/service.yaml"
    

This time you should see Specmatic load your canned response file also.

Loading service.yaml
API Specification Summary: service.yaml
  OpenAPI Version: 3.0.1
  API Paths: 1, API Operations: 1

  Loading stub expectations from /Users/harikrishnan/projects/agilefaqs/ContractTesting/ExamplesAsTestAndStub/service_data
  Reading the following stub files:
    /Users/harikrishnan/projects/agilefaqs/ContractTesting/ExamplesAsTestAndStub/service_data/togo.json

Stub server is running on http://0.0.0.0:9000. Ctrl + C to stop.

Once the stub server is running you can verify the API by accessing it through Postman, Chrome, Curl etc.

curl http://localhost:9000/pets/2

You should now be able to see the data pertaining to the togo.json file that you added.

{
    "id": 2,
    "name": "Togo",
    "type": "Siberian Husky",
    "status": "Adopted"
}

Specmatic validates this externalised stub JSON file togo.json against the service.yaml. Let us try this by removing the status field within http-response body in togo.json and run the stub command again.

  • specmatic stub service.yaml
    
  • npx specmatic stub service.yaml
    
  • # Please note docker command here has to volume map the directory containing service.yaml 
    # to a directory within the container so that both service.yaml and folder service_data along 
    # with togo.json are available to Specmatic docker container
    docker run -v "/local-directory/:/specs" -p 9000:9000 znsio/specmatic stub "/specs/service.yaml"
    

You should see an output like below.

Loading stub expectations from /Users/harikrishnan/projects/agilefaqs/ContractTesting/ExamplesAsTestAndStub/service_data
  Reading the following stub files:
    /Users/harikrishnan/projects/agilefaqs/ContractTesting/ExamplesAsTestAndStub/service_data/togo.json
  /Users/harikrishnan/projects/agilefaqs/ContractTesting/ExamplesAsTestAndStub/service_data/togo.json didn't match service.yaml
    Error from contract service.yaml
  
      In scenario "Should be able to get a pet by petId. Response: Should be able to get a pet by petId"
      API: GET /pets/(petid:number) -> 200
  
        >> RESPONSE.BODY.status
  
           Key named status in the contract was not found in the stub

Stub server is running on http://0.0.0.0:9000. Ctrl + C to stop.

Specmatic again rejects the expectation / canned response since it is not in line with the OpenAPI Specification.

We can now start consumer development against this stub without any dependency on the real API.

To know more about Intelligent Service Virtualisation please refer to below video demos

Learn more about Stubbing / Smart Mocks here.