Setting up a mock response for API testing

Question

Pulumi · Accepted Answer

When setting up a mock response for API testing in AWS using Pulumi, you can utilize AWS API Gateway to create and configure a mock integration. This mock integration allows you to respond to API requests with predefined responses, which is helpful for testing frontend applications or during the initial stages of backend development when the actual backend is not yet implemented.

In this Pulumi program, we will create the necessary AWS API Gateway components to set up a mock response. This includes a REST API, a resource (like an endpoint), a method (e.g., GET, POST), an integration that specifies it's a MOCK type, and finally, the method response and integration response to define the desired mock output.

Here's how to accomplish this in TypeScript:

1. `aws.apigateway.RestApi` - to create a new REST API.
2. `aws.apigateway.Resource` - to create a new resource representing our endpoint.
3. `aws.apigateway.Method` - to attach an HTTP method to our resource.
4. `aws.apigateway.Integration` - to set up the MOCK integration with the resource and method.
5. `aws.apigateway.MethodResponse` & `aws.apigateway.IntegrationResponse` - to define the structure and content of the response we want to return when the endpoint is hit.

Let's implement this in a Pulumi program:

```typescript
import * as aws from "@pulumi/aws";

// Create an API Gateway REST API
const api = new aws.apigateway.RestApi("example-api", {
    description: "Example REST API for testing mock responses",
});

// Create a resource (endpoint)
const resource = new aws.apigateway.Resource("example-resource", {
    restApi: api.id,
    pathPart: "example", // the part of the path. e.g., in "example.com/example", this is "example"
    parentId: api.rootResourceId, // retrieve the root resource to attach this new resource (endpoint)
});

// Define the HTTP method for the endpoint (e.g., GET request)
const method = new aws.apigateway.Method("example-method", {
    restApi: api.id,
    resourceId: resource.id,
    httpMethod: "GET",
    authorization: "NONE", // No authorization for simplicity
});

// Define a MOCK integration for the method
const integration = new aws.apigateway.Integration("example-integration", {
    restApi: api.id,
    resourceId: resource.id,
    httpMethod: method.httpMethod,
    type: "MOCK", // Specify the integration type as MOCK
    requestTemplates: {
        "application/json": "{\"statusCode\": 200}" // Response template for the mock integration
    },
});

// Define the method response
const methodResponse = new aws.apigateway.MethodResponse("example-method-response", {
    restApi: api.id,
    resourceId: resource.id,
    httpMethod: method.httpMethod,
    statusCode: "200", // Status code for the successful response
    responseModels: {
        "application/json": "Empty", // Specify the response model, "Empty" is a default model
    },
});

// Define the integration response, which returns the mock data
const integrationResponse = new aws.apigateway.IntegrationResponse("example-integration-response", {
    restApi: api.id,
    resourceId: resource.id,
    httpMethod: method.httpMethod,
    statusCode: methodResponse.statusCode,
    responseTemplates: {
        "application/json": "{\"message\": \"Hello, World!\"}", // Mock response body
    },
});

// Export the invoke URL of the REST API
export const invokeUrl = api.executionArn.apply(executionArn =>
    `https://${executionArn}.execute-api.${aws.config.region}.amazonaws.com/`
);
```

Explanation:
- We first create a REST API, which acts as a container for the resources (endpoints) we will define.
- We add a resource to our REST API that represents an endpoint, which is the part of the URL that identifies this specific endpoint within our API.
- We then define an HTTP method for the API resource. In this case, we're creating a GET method, which specifies that our resource will respond to HTTP GET requests.
- An integration is created for the resource and method. We set the integration type to MOCK, which indicates that it's not actually integrating with a real backend service.
- The `requestTemplates` within the integration is where we can define what the mock response should be. It's a mapping of content types to response templates.
- Method and integration responses specify the structure and content of the response that the client receives. In this case, it's a simple JSON object with a message.
- Finally, we export the invoke URL for the API, which you can use to test the mock response.

This program sets up everything in AWS necessary to simulate responses for API testing. You can now invoke your API's endpoints, and you will receive the mock responses defined in the program.

Remember to install the required Pulumi AWS package before running this program by using:

```shell
npm install @pulumi/aws
```

After setting up your [AWS credentials](https://www.pulumi.com/registry/packages/aws/installation-configuration/), you can run `pulumi up` to deploy this code.