If httr makes HTTP easy and testthat makes testing fun, httptest makes testing your code that uses HTTP a simple pleasure.
Details
The httptest package lets you test R code that wraps an API without
requiring access to the remote service. It provides three test contexts
that mock the network connection in different ways. with_mock_api() lets
you provide custom fixtures as responses to requests, stored as plain-text
files in your test directory. without_internet() converts HTTP requests
into errors that print the request method, URL, and body payload, if
provided, allowing you to assert that a function call would make a
correctly-formed HTTP request or assert that a function does not make a
request (because if it did, it would raise an error in this context).
with_fake_http() raises a "message" instead of an "error", and HTTP
requests return a "response"-class object. Like without_internet, it allows
you to assert that the correct requests were (or were not) made, but it
doesn't cause the code to exit with an error.
httptest offers additional expectations to assert that HTTP requests
were---or were not---made. expect_GET(), expect_PUT(), expect_PATCH(),
expect_POST(), and expect_DELETE() assert that the specified HTTP request
is made within one of the test contexts. They catch the error or message
raised by the mocked HTTP service and check that the request URL and optional
body match the expectation. expect_no_request() is the inverse of those: it
asserts that no error or message from a mocked HTTP service is raised.
expect_header() asserts that an HTTP request, mocked or not, contains a
request header. expect_json_equivalent() checks that two R objects would
generate equivalent JSON, taking into account how JSON objects are unordered
whereas R named lists are ordered.
For an overview of testing with httptest, see vignette("httptest").
The package also includes capture_requests(), a context that collects the
responses from requests you make and stores them as mock files. This enables
you to perform a series of requests against a live server once and then build
your test suite using those mocks, running your tests in with_mock_api.
When recording requests, by default httptest looks for and redacts the
standard ways that auth credentials are passed in requests. This prevents you
from accidentally publishing your personal tokens. The redacting behavior is
fully customizable, either by providing a function (response) {...} to
set_redactor(), or by placing a function in your package's
inst/httptest/redact.R that will be used automatically any time you record
requests with your package loaded. See vignette("redacting") for details.
httptest also enables you to write package vignettes and other R Markdown
documents that communicate with a remote API. By adding as little as
start_vignette() to the beginning of your vignette, you can safely record
API responses from a live session, using your secret credentials. These API
responses are scrubbed of sensitive personal information and stored in a
subfolder in your vignettes directory. Subsequent vignette builds,
including on continuous-integration services, CRAN, and your package users'
computers, use these recorded responses, allowing the document to regenerate
without a network connection or API credentials. To record fresh API
responses, delete the subfolder of cached responses and re-run. See
vignette("vignettes") for more discussion and links to examples.