HTTP proxy that generates and loads from fixtures for testing.

pip install testypie==1.2.2



A test helper service that autogenerates your fixtures by recording real HTTP requests in order to replay them.

The main advantage is that it is agnostic to what underlying HTTP library you are using (or even what programming language you are using).

It works as a distinct proxy but can also be used as a library in Python tests, e.g. combined with HTTPretty.



To run standalone (suitable for testing in any language):

$ pip install testypie
$ testypie
 * Serving Flask app "testypie" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on (Press CTRL+C to quit)

Then run your tests with HTTP_PROXY set:

$ export HTTP_PROXY=
$ # e.g. mocha mytests.js or pytest

How it works

Whether used as a proxy or as an intercept within Python tests, the idea is that you follow the given workflow:

  • Write unit tests that exercise your code without even attempting to mock
  • Your code will result in an HTTP request that is allowed to happen over the real network on first run only
  • A realistic fixture from this real request is stored in $PWD/fixtures
  • On the next test run, testypie will respond with the fixture on disk rather than allow the real request to happen
  • Now your tests work fine offline
  • You are free to modify fixtures (see fixture format below) to make it replay an altered or stub version of the response
  • At any time, you can delete individual or all fixtures to "refresh" them (e.g. if the upstream API changes) -- no need to maintain manual mocks to keep them aligned with upstreams

Use cases and motivation

This project came out of writing tests for code in domains involving a lot of data. For example, working with data from DBPedia or other large data sources.

With testypie, you can simply write tests pointing at real data URLs and worry less about having to generate (and maintain) a collection of mocks, stubs or full fixtures.

It is especially useful when using libraries that do HTTP under the hood, but the precise HTTP library used is abstracted away from you, so it is difficult to mock effectively. Examples of this are rdflib or boto.

In the case of boto and AWS, testypie is useful in capturing exactly what boto and AWS do and replaying it rather than having to reverse engineer a fairly complex API so that you can mock it.

Fixture Format

Fixtures are a model of the HTTP response (code, headers, body) serialised to YAML files. The use of YAML was a deliberate choice such that the multiline string support allows for a clear, intuitive way to capture the response body exactly as it was (including all newlines) such that it can be easily edited.

Even in cases where an upstream responded with e.g. JSON with no newlines, you are pretty to alter the fixture to respond instead with pretty-printed JSON for easier editing.

The file names for fixtures are based on the HTTP method then a percent-encoded form of the URL that was fetched. This both allows for different responses for different methods (e.g. PUT vs. DELETE) and also keeps the file names understandable enough such that it would be possible to generate fixtures up front with a script (or manually).


The main limitation is the lack of mocking HTTPS in standalone mode. It works fine when used as a helper library in Python though.

Additionally, fixtures are currently keyed against HTTP method and URL only, so there is no way to temporarily mock a service to respond with e.g. HTTP 503 and then mock is back to a healthy HTTP 200 response. For this use case, traditional mocking may be more appropriate as testypie is focused on use cases where you are mocking data sources or capturing more complex APIs (e.g. AWS APIs) where recreating and maintaining mocks would be a lot of effort.

This also means that there is no support for content negotiation or other cases where a response would vary according to request headers.