ExVCR

Record and replay HTTP interactions library for Elixir. It's inspired by Ruby's VCR (https://github.com/vcr/vcr), and trying to provide similar functionalities.

Basics

The following HTTP libraries can be applied.

ibrowse-based libraries.
- HTTPotion
hackney-based libraries.
- HTTPoison
- support is very limited, and tested only with sync request of HTTPoison yet.
httpc-based libraries.
- erlang-oauth
- tirexs
- support is very limited, and tested only with :httpc.request/1 and :httpc.request/4.

HTTP interactions are recorded as JSON file. The JSON file can be recorded automatically (vcr_cassettes) or manually updated (custom_cassettes).

Notes

ExVCR.Config functions must be called from setup or test. Calls outside of test process, such as in setup_all will not work.

Install

Add :exvcr to deps section of mix.exs.

def deps do
  [ {:exvcr, "~> 0.11", only: :test} ]
end

Optionally, preferred_cli_env: [vcr: :test] can be specified for running mix vcr in :test env by default.

def project do
  [ ...
    preferred_cli_env: [
      vcr: :test, "vcr.delete": :test, "vcr.check": :test, "vcr.show": :test
    ],
    ...
end

Usage

Add use ExVCR.Mock to the test module. This mocks ibrowse by default. For using hackney, specify adapter: ExVCR.Adapter.Hackney options as follows.

Example with ibrowse

defmodule ExVCR.Adapter.IBrowseTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock

  setup do
    ExVCR.Config.cassette_library_dir("fixture/vcr_cassettes")
    :ok
  end

  test "example single request" do
    use_cassette "example_ibrowse" do
      :ibrowse.start
      {:ok, status_code, _headers, body} = :ibrowse.send_req('http://example.com', [], :get)
      assert status_code == '200'
      assert to_string(body) =~ ~r/Example Domain/
    end
  end

  test "httpotion" do
    use_cassette "example_httpotion" do
      HTTPotion.start
      assert HTTPotion.get("http://example.com", []).body =~ ~r/Example Domain/
    end
  end
end

Example with hackney

defmodule ExVCR.Adapter.HackneyTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock, adapter: ExVCR.Adapter.Hackney

  setup_all do
    HTTPoison.start
  end

  test "get request" do
    use_cassette "httpoison_get" do
      assert HTTPoison.get!("http://example.com").body =~ ~r/Example Domain/
    end
  end
end

Example with httpc

defmodule ExVCR.Adapter.HttpcTest do
  use ExUnit.Case, async: true
  use ExVCR.Mock, adapter: ExVCR.Adapter.Httpc

  setup_all do
    :inets.start
  end

  test "get request" do
    use_cassette "example_httpc_request" do
      {:ok, result} = :httpc.request('http://example.com')
      {{_http_version, _status_code = 200, _reason_phrase}, _headers, body} = result
      assert to_string(body) =~ ~r/Example Domain/
    end
  end

Custom Cassettes

You can manually define custom cassette JSON file for more flexible response control rather than just recoding the actual server response.

Optional 2nd parameter of ExVCR.Config.cassette_library_dir method specifies the custom cassette directory. The directory is separated from vcr cassette one for avoiding mistakenly overwriting.
Adding custom: true option to use_cassette macro indicates to use the custom cassette, and it just returns the pre-defined JSON response, instead of requesting to server.

defmodule ExVCR.MockTest do
  use ExUnit.Case, async: true
  import ExVCR.Mock

  setup do
    ExVCR.Config.cassette_library_dir("fixture/vcr_cassettes", "fixture/custom_cassettes")
    :ok
  end

  test "custom with valid response" do
    use_cassette "response_mocking", custom: true do
      assert HTTPotion.get("http://example.com", []).body =~ ~r/Custom Response/
    end
  end

The custom JSON file format is the same as vcr cassettes.

fixture/custom_cassettes/response_mocking.json

[
  {
    "request": {
      "url": "http://example.com"
    },
    "response": {
      "status_code": 200,
      "headers": {
        "Content-Type": "text/html"
      },
      "body": "<h1>Custom Response</h1>"
    }
  }
]

Recording VCR Cassettes

Matching

ExVCR uses URL parameter to match request and cassettes. The url parameter in the JSON file is taken as regexp string.

Removing Sensitive Data

ExVCR.Config.filter_sensitive_data(pattern, placeholder) method can be used to remove sensitive data. It searches for string matches with pattern, which is a string representing a regular expression, and replaces with placeholder. Replacements happen both in URLs and request and response bodies.

test "replace sensitive data" do
  ExVCR.Config.filter_sensitive_data("<PASSWORD>.+</PASSWORD>", "PLACEHOLDER")
  use_cassette "sensitive_data" do
    assert HTTPotion.get("http://something.example.com", []).body =~ ~r/PLACEHOLDER/
  end
end

ExVCR.Config.filter_request_headers(header) and ExVCR.Config.filter_request_options(option) can be used to remove sensitive data in the request headers. It checks if the header is found in the request headers and blanks out it's value with ***.

test "replace sensitive data in request header" do
  ExVCR.Config.filter_request_headers("X-My-Secret-Token")
  use_cassette "sensitive_data_in_request_header" do
    body = HTTPoison.get!("http://localhost:34000/server?", ["X-My-Secret-Token": "my-secret-token"]).body
    assert body == "test_response"
  end

  # The recorded cassette should contain replaced data.
  cassette = File.read!("#{@dummy_cassette_dir}/sensitive_data_in_request_header.json")
  assert cassette =~ "\"X-My-Secret-Token\": \"***\""
  refute cassette =~  "\"X-My-Secret-Token\": \"my-secret-token\""

  ExVCR.Config.filter_request_headers(nil)
end

test "replace sensitive data in request options" do
  ExVCR.Config.filter_request_options("basic_auth")
  use_cassette "sensitive_data_in_request_options" do
    body = HTTPoison.get!(@url, [], [hackney: [basic_auth: {"username", "password"}]]).body
    assert body == "test_response"
  end

  # The recorded cassette should contain replaced data.
  cassette = File.read!("#{@dummy_cassette_dir}/sensitive_data_in_request_options.json")
  assert cassette =~ "\"basic_auth\": \"***\""
  refute cassette =~  "\"basic_auth\": {\"username\", \"password\"}"

  ExVCR.Config.filter_request_options(nil)
end

Ignoring query params in URL

If ExVCR.Config.filter_url_params(true) is specified, query params in URL will be ignored when recording cassettes.

test "filter url param flag removes url params when recording cassettes" do
  ExVCR.Config.filter_url_params(true)
  use_cassette "example_ignore_url_params" do
    assert HTTPotion.get(
      "http://localhost:34000/server?should_not_be_contained", []).body =~ ~r/test_response/
  end
  json = File.read!("#{__DIR__}/../#{@dummy_cassette_dir}/example_ignore_url_params.json")
  refute String.contains?(json, "should_not_be_contained")

Removing headers from response

If ExVCR.Config.response_headers_blacklist(headers_blacklist) is specified, the headers in the list will be removed from the response.

test "remove blacklisted headers" do
  use_cassette "original_headers" do
    assert Map.has_key?(HTTPoison.get!(@url, []).headers, "connection") == true
  end

  ExVCR.Config.response_headers_blacklist(["Connection"])
  use_cassette "remove_blacklisted_headers" do
    assert Map.has_key?(HTTPoison.get!(@url, []).headers, "connection") == false
  end

  ExVCR.Config.response_headers_blacklist([])
end

Matching Options

Matching against query params

By default, query params are not used for matching. In order to include query params, specify match_requests_on: [:query] for use_cassette call.

test "matching query params with match_requests_on params" do
  use_cassette "different_query_params", match_requests_on: [:query] do
    assert HTTPotion.get("http://localhost/server?p=3", []).body =~ ~r/test_response3/
    assert HTTPotion.get("http://localhost/server?p=4", []).body =~ ~r/test_response4/
  end
end

Matching against request body

By default, request body is not used for matching. In order to include request body, specify match_requests_on: [:request_body] for use_cassette call.

test "matching request body with match_requests_on params" do
  use_cassette "different_request_body_params", match_requests_on: [:request_body] do
    assert HTTPotion.post("http://localhost/server", [body: "p=3"]).body =~ ~r/test_response3/
    assert HTTPotion.post("http://localhost/server", [body: "p=4"]).body =~ ~r/test_response4/
  end
end

Matching against custom parameters

You can define and use your own matchers for cases not covered by the build-in matchers. To do this you can specify custom_matchers: [func_one, func_two, ...] for use_cassette call.

test "matching special header with custom_matchers" do
  matches_special_header = fn response, keys, _recorder_options ->
    recorded_headers = always_map(response.request.headers)
    expected_value = recorded_headers["X-Special-Header"]
    keys[:headers]
    |> Enum.any?(&(match?({"X-Special-Header", ^expected_value}, &1)))
  end

  use_cassette "special_header_match", custom_matchers: [matches_special_header] do
    # These two requests will match with each other since our custom matcher matches (even if without matching all headers)
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "My App", "X-Special-Header": "Value One"]]).body =~ ~r/test_response_one/
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "Other App", "X-Special-Header": "Value One"]]).body =~ ~r/test_response_one/

    # This will not match since the header has a different value:
    assert HTTPotion.post("http://localhost/server",
        [headers: ["User-Agent": "My App", "X-Special-Header": "Value Two"]]).body =~ ~r/test_response_two/
  end
end

Default Config

Default parameters for ExVCR.Config module can be specified in config\config.exs as follows.

use Mix.Config

config :exvcr, [
  vcr_cassette_library_dir: "fixture/vcr_cassettes",
  custom_cassette_library_dir: "fixture/custom_cassettes",
  filter_sensitive_data: [
    [pattern: "<PASSWORD>.+</PASSWORD>", placeholder: "PASSWORD_PLACEHOLDER"]
  ],
  filter_url_params: false,
  filter_request_headers: [],
  response_headers_blacklist: []
]

If exvcr is defined as test-only dependency, describe the above statement in test-only config file (ex. config\test.exs) or make it conditional (ex. wrap with if Mix.env == :test).

Global mock experimental feature

The global mock is an attempt to address a general issue with exvcr being slow, see #107

In general, every use_cassette takes around 500 ms so if you extensively use cassettes it could spend minutes doing :meck.expect/2 and :meck.unload/1. Even exvcr tests need 40 seconds versus 1 second when global mock is used.

Since feature is experimental be careful when using it. Please note the following:

ExVCR implements global mock, which means that all HTTP client calls outside of use_cassette go through meck.passthough/1.
There are some report that the feature doesn't work in some case, see the issue.
By default, the global mocking disabled, to enabled it set the following in config:

use Mix.Config

config :exvcr, [
  global_mock: true
]

All tests that are written for exvcr could also be running in global mocking mode:

$ GLOBAL_MOCK=true mix test

.........................................................

Finished in 1.3 seconds
141 tests, 0 failures

Randomized with seed 905427

Mix Tasks

The following tasks are added by including exvcr package.

mix vcr
mix vcr.delete
mix vcr.check
mix vcr.show
mix vcr --help

[mix vcr] Show cassettes

$ mix vcr
Showing list of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Last Update]
  example_httpotion.json                   2013/11/07 23:24:49
  example_ibrowse.json                     2013/11/07 23:24:49
  example_ibrowse_multiple.json            2013/11/07 23:24:48
  httpotion_delete.json                    2013/11/07 23:24:47
  httpotion_patch.json                     2013/11/07 23:24:50
  httpotion_post.json                      2013/11/07 23:24:51
  httpotion_put.json                       2013/11/07 23:24:52

Showing list of cassettes in [fixture/custom_cassettes]
  [File Name]                              [Last Update]
  method_mocking.json                      2013/10/06 22:05:38
  response_mocking.json                    2013/09/29 17:23:38
  response_mocking_regex.json              2013/10/06 18:13:45

[mix vcr.delete] Delete cassettes

The mix vcr.delete task deletes the cassettes that contains the specified pattern in the file name.

$ mix vcr.delete ibrowse
Deleted example_ibrowse.json.
Deleted example_ibrowse_multiple.json.

If -i (--interactive) option is specified, it asks for confirmation before deleting each file.

$ mix vcr.delete ibrowse -i
delete example_ibrowse.json? y
Deleted example_ibrowse.json.
delete example_ibrowse_multiple.json? y
Deleted example_ibrowse_multiple.json.

If -a (--all) option is specified, all the cassettes in the specified folder becomes the target for delete.

[mix vcr.check] Check cassettes

The mix vcr.check shows how many times each cassette is applied while executing mix test tasks. It is intended for verifying the cassettes are properly used. [Cassette Counts] indicates the count that the pre-recorded JSON cassettes are applied. [Server Counts] indicates the count that server access is performed.

$ mix vcr.check
...............................
31 tests, 0 failures
Showing hit counts of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  example_httpotion.json                   1                    0
  example_ibrowse.json                     1                    0
  example_ibrowse_multiple.json            2                    0
  httpotion_delete.json                    1                    0
  httpotion_patch.json                     1                    0
  httpotion_post.json                      1                    0
  httpotion_put.json                       1                    0
  sensitive_data.json                      0                    2
  server1.json                             0                    2
  server2.json                             2                    2

Showing hit counts of cassettes in [fixture/custom_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  method_mocking.json                      1                    0
  response_mocking.json                    1                    0
  response_mocking_regex.json              1                    0

The target test file can be limited by specifying test files, as similar as mix test tasks.

$ mix vcr.check test/exvcr_test.exs
.............
13 tests, 0 failures
Showing hit counts of cassettes in [fixture/vcr_cassettes]
  [File Name]                              [Cassette Counts]    [Server Counts]
  example_httpotion.json                   1                    0
...
...

[mix vcr.show] Show cassettes

The mix vcr.show task displays the contents of cassettes JSON file in the prettified format.

$ mix vcr.show fixture/vcr_cassettes/httpoison_get.json
[
  {
    "request": {
      "url": "http://example.com",
      "headers": [],
      "method": "get",
      "body": "",
      "options": []
    },
...

[mix vcr --help] Help

Displays helps for mix sub-tasks.

$ mix vcr --help
Usage: mix vcr [options]
  Used to display the list of cassettes

  -h (--help)         Show helps for vcr mix tasks
  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory

Usage: mix vcr.delete [options] [cassete-file-names]
  Used to delete cassettes

  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory
  -i (--interactive)  Request confirmation before attempting to delete
  -a (--all)          Delete all the files by ignoring specified [filenames]

Usage: mix vcr.check [options] [test-files]
  Used to check cassette use on test execution

  -d (--dir)          Specify vcr cassettes directory
  -c (--custom)       Specify custom cassettes directory

Usage: mix vcr.show [cassete-file-names]
  Used to show cassette contents

Notes

If the cassette save directory is changed from the default, [-d, --dir] option (for vcr cassettes) and [-c, --custom] option (for custom cassettes) can be used to specify the directory.

IEx Helper

ExVCR.IEx module provides simple helper functions to display the HTTP request/response in JSON format, instead of recording in the cassette files.

% iex -S mix
Erlang R16B03 (erts-5.10.4) ...
Interactive Elixir (0.12.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require ExVCR.IEx
nil
iex(2)> ExVCR.IEx.print do
...(2)>   :ibrowse.send_req('http://example.com', [], :get)
...(2)> end
[
  {
    "request": {
      "url": "http://example.com",
      "headers": [],
      "method": "get",
      "body": "",
      "options": []
    },
    "response": {
      "type": "ok",
      "status_code": 200,
...

The adapter option can be specified as adapter argument of print function, as follows.

% iex -S mix
Erlang R16B03 (erts-5.10.4) ...

Interactive Elixir (0.12.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require ExVCR.IEx
nil
iex(2)> ExVCR.IEx.print(adapter: ExVCR.Adapter.Hackney) do
...(2)>   HTTPoison.get!("http://example.com").body
...(2)> end
[
  {
    "request": {
      "url": "http://example.com",
...

Stubbing Response

Specifying :stub as fixture name allows directly stubbing the response header/body information based on parameter.

test "stub request works for HTTPotion" do
  use_cassette :stub, [url: "http://example.com", body: "Stub Response", status_code: 200] do
    response = HTTPotion.get("http://example.com", [])
    assert response.body =~ ~r/Stub Response/
    assert response.headers[:"Content-Type"] == "text/html"
    assert response.status_code == 200
  end
end

test "stub request works for HTTPoison" do
  use_cassette :stub, [url: "http://www.example.com", body: "Stub Response"] do
    response = HTTPoison.get!("http://www.example.com")
    assert response.body =~ ~r/Stub Response/
    assert response.headers["Content-Type"] == "text/html"
    assert response.status_code == 200
  end
end

test "stub request works for httpc" do
  use_cassette :stub, [url: "http://www.example.com",
                       method: "get",
                       status_code: ["HTTP/1.1", 200, "OK"],
                       body: "success!"] do

  {:ok, result} = :httpc.request('http://example.com')
  {{_http_version, _status_code = 200, _reason_phrase}, _headers, body} = result
  assert to_string(body) == "success!"
end

If the specified :url parameter doesn't match requests called inside the use_cassette block, it raises ExVCR.InvalidRequestError.

The :url can be regular expression string. Please note that you should use the ~r sigil with / as delimiters.

test "match URL with regular expression" do
  use_cassette :stub, [url: "~r/(foo|bar)/", body: "Stub Response", status_code: 200] do
    # ...
  end
end

test "make sure to properly escape the /" do
  # escape /path/to/file
  use_cassette :stub, [url: "~r/\/path\/to\/file", body: "Stub Response", status_code: 200] do
    # ...
  end
end

test "the sigil delimiter cannot be anything else" do
  use_cassette :stub, [url: "~r{this-delimiter-doesn-not-work}", body: "Stub Response", status_code: 200] do
    # ...
  end
end

TODO

Improve performance, as it's very slow.

FortAwesome / exvcr

ExVCR

Basics

Notes

Install

Usage

Example with ibrowse

Example with hackney

Example with httpc

Custom Cassettes

Recording VCR Cassettes

Matching

Removing Sensitive Data

Ignoring query params in URL

Removing headers from response

Matching Options

Matching against query params

Matching against request body

Matching against custom parameters

Default Config

Global mock experimental feature

Mix Tasks

[mix vcr] Show cassettes

[mix vcr.delete] Delete cassettes

[mix vcr.check] Check cassettes

[mix vcr.show] Show cassettes

[mix vcr --help] Help

Notes

IEx Helper

Stubbing Response

TODO

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