Assert Request Data

MSW provides a great way to test api calls without getting stuck in implementation details. One thing however that is missing is the ability to assert on request data. This can be done in a custom resolver, but we think it is important enough we have made it a first class citizen.

One way to think of this is by asking the question:

If I change the logic in a certain part of the application, should my tests fail?

Usually the answer is yes. So tying this back, if we were to change the transformation logic that outputs the data so that the wrong data is accidentally sent as part of the api call, should the test fail? We think it should.

Example

Note: The id key in the withParams here matches the :id argument in the post url

when(post("https://some.url/:id")).thenReturnFor(
  request(
    withBody({ foo: "bar" }),
    withHeaders({ "content-type": "application/json" }),
    withParams({ id: "expected-id" })
  ),
  ok({ response: "success" })
);

In the above request, the resolver will only match if the request data matches the request specified.

Example#

Example