Pact-jest (js) with docment upload (multipart-form)

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Summary

The issue at hand is creating a Pact test for a backend service that handles file uploads using multipart/form-data. The service is generated from an API specification using OpenAPI Generator, and the goal is to define a Pact interaction that accurately represents the file upload request.

Root Cause

The root cause of the problem lies in the difficulty of defining the multipart/form-data body in the Pact interaction. The builder.multipartBody method requires a file name, which can be challenging to specify when working with Pact.

Why This Happens in Real Systems

This issue occurs in real systems because:

  • Pact is designed to work with JSON bodies by default
  • Multipart/form-data requests require a specific format and boundary definition
  • The builder.multipartBody method has limitations when it comes to specifying file names and boundaries

Real-World Impact

The real-world impact of this issue includes:

  • Inability to accurately test file upload functionality using Pact
  • Potential errors or inconsistencies in the Pact interaction definition
  • Difficulty in ensuring that the backend service handles file uploads correctly

Example or Code

new PactV4({
  consumer: 'CONSUMER',
  provider: 'PROVIDER',
  logLevel: 'debug',
})
.addInteraction()
.uponReceiving('uploading a document')
.withRequest('POST', '/document', builder => {
  builder.headers({
    'Content-Type': MatchersV3.regex('multipart/form-data; boundary=.*', 'multipart/form-data; boundary=test'),
  });
  builder.multipartBody({
    file: MatchersV3.like({
      filename: 'example.txt',
      contentType: 'text/plain',
      body: 'Hello World!',
    }),
  });
})
.willRespondWith(200, builder => {
  builder.jsonBody(MatchersV3.like(response));
});

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Using the builder.multipartBody method with a carefully defined file object
  • Ensuring that the Content-Type header is correctly set to multipart/form-data with a valid boundary
  • Utilizing Pact‘s built-in support for multipart/form-data requests

Why Juniors Miss It

Juniors may miss this issue due to:

  • Lack of experience with Pact and multipart/form-data requests
  • Insufficient understanding of the Pact interaction definition
  • Difficulty in specifying the file name and boundary in the builder.multipartBody method

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