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Sometimes your tests using a vcr cassette will fail and you will want to debug them.

An HTTP request has been made that vcr does not know how to handle

If you get an error starting with “An HTTP request has been made that vcr does not know how to handle:” when running your tests, it means that the code in your test makes an HTTP request for which there is no matching information in the cassette you are using. You might have added a request, or changed one slightly.

The easy fix is: delete the cassette and re-run the test to re-record the cassette. Run the test a second time to ensure all is well. If not, escalate to the next paragraph.

Maybe you didn’t actually want to change the request you are making. Make sure the requests do not contain something random, or something related to e.g. what time it is now, in the URI ( To make sure things are not varying, you might want to use mocking (of e.g. a function returning the current time), setting a random seed, using withr (for e.g. setting an option to a certain value in your test).

Actual debugging

Ideally you will want to run the code of the tests as if it were run inside tests, in particular, using the same vcr cassette.

Prepare your debugging environment

You will first need to load either the vcr helper tests/testthat/helper-vcr.R (e.g. via devtools::load_all()) or source the vcr setup file tests/testthat/setup-vcr.R i.e. the file with these lines (and maybe others)

  dir = vcr::vcr_test_path("fixtures"),
  filter_sensitive_data = list("<<github_api_token>>" = Sys.getenv('GITHUB_PAT'))

If instead of vcr::vcr_test_path("fixtures") you see "../fixtures", replace "../fixtures" with vcr::vcr_test_path("fixtures"), as vcr::vcr_test_path() is a function that is meant to help exactly what you will want: have the path to tests/fixtures/ work from tests and from the root (which is where you will be running the code to debug it).

So that is one step (loading the vcr helper or sourcing the vcr setup file), or maybe two (if you also had to replace "../fixtures" with vcr::vcr_test_path("fixtures")).

Debugging itself

Now look at the test whose code you are trying to debug e.g.

foo <- function() crul::ok('')

test_that("foo works", {
  vcr::use_cassette("testing", {
    x <- foo()

If you want to run the code as if you were in the test,

foo <- function() crul::ok('')
vcr::insert_cassette("testing") # it will be created if needed
x <- foo()
# further interactive debugging and fixes


You can use vcr’s built in logging to help in your debugging process. To configure logging, use the vcr_configure() function, and set log=TRUE and set options for logging on the log_opts parameter as a named list. See ?vcr_configure for details.

Here, we are setting our log file to be a temporary file that will be cleaned up at the end of the R session. Here, the file extension is .log, but the file extension does not matter.

  dir = vcr::vcr_test_path("fixtures"),
  log = TRUE,
  log_opts = list(file = file.path(tempdir(), "vcr.log"))

With log=TRUE you can continue with debugging. Open the log file you set in a text editor or other location; or examine in your shell/terminal.

As an example, after running the block above

foo <- function() crul::ok('')

test_that("foo works", {
  vcr::use_cassette("testing", {
    x <- foo()

If we open the log file we’ll see the logs for each step vcr takes in handling an HTTP request. The logs have information on what cassette was used, what exact time it was recorded, what matchers were in use, the cassette options, and how a request is handled.

[Cassette: 'testing'] - 2020-11-24 16:05:17 - Init. HTTPInteractionList w/ request matchers [method, uri] & 0 interaction(s): {  }
[Cassette: 'testing'] - 2020-11-24 16:05:17 - Initialized with options: {name: testing, record: once, serialize_with: yaml, persist_with: FileSystem, match_requests_on: c("method", "uri"), update_content_length_header: FALSE, allow_playback_repeats: FALSE, preserve_exact_body_bytes: FALSE}
[Cassette: 'testing'] - 2020-11-24 16:05:17 - Handling request: head (disabled: FALSE)
[Cassette: 'testing'] - 2020-11-24 16:05:17 - Identified request type: (recordable) for head
[Cassette: 'testing'] - 2020-11-24 16:05:17 -    Recorded HTTP interaction: head => 200 

Logging isn’t meant to be turned on all the time - rather only for debugging/informational purposes.

Return to normal development

Make sure you ejected the cassette you were using!

Unless your vcr helper/setup file tweaked more things than you would like, you do not even need to re-start R, but you could, just to be on the safe side.