Better document the ignore_urls setting (#187)

* Allow append to be passed to a previously nil setting

* Update README with ignore_urls instructions

README.md

@@ -270,6 +270,22 @@ test "replace sensitive data in request options" do
 end
 ```
 
+#### Allowed hosts
+
+The `:ignore_urls` can be used to allow requests to be made to certain hosts.
+
+```elixir
+setup do
+  ExVCR.Setting.set(:ignore_urls, [~/example.com/])
+  ExVCR.Setting.append(:ignore_urls, ~/anotherurl.com/)
+end
+
+test "an actual request is made to example.com" do
+  HTTPoison.get!("https://example.com/path?query=true")
+  HTTPoison.get!("https://anotherurl.com/path?query=true")
+end
+```
+
 #### Ignoring query params in URL
 
 If `ExVCR.Config.filter_url_params(true)` is specified, query params in URL

lib/exvcr/setting.ex

@@ -14,7 +14,10 @@ defmodule ExVCR.Setting do
   end
 
   def append(key, value) do
-    set(key, [value | ExVCR.Setting.get(key)])
+    case __MODULE__.get(key) do
+      [_ | _] = values -> __MODULE__.set(key, [value | values])
+      _ -> __MODULE__.set(key, [value])
+    end
   end
 
   defp setup do

test/setting_test.exs

@@ -27,4 +27,20 @@ defmodule ExVCR.SettingTest do
     ExVCR.Setting.set(:response_headers_blacklist, ["Content-Type", "Accept"])
     assert ExVCR.Setting.get(:response_headers_blacklist) == ["Content-Type", "Accept"]
   end
+
+  test "set ignore_urls" do
+    ExVCR.Setting.set(:ignore_urls, ["example.com"])
+    assert ExVCR.Setting.get(:ignore_urls) == ["example.com"]
+  end
+
+  test "append ignore_urls when there are no existing values" do
+    ExVCR.Setting.append(:ignore_urls, "example.com")
+    assert ExVCR.Setting.get(:ignore_urls) == ["example.com"]
+  end
+
+  test "append ignore_urls when there are existing values" do
+    ExVCR.Setting.set(:ignore_urls, [~r/example.com/])
+    ExVCR.Setting.append(:ignore_urls, ~r/example2.com/)
+    assert ExVCR.Setting.get(:ignore_urls) == [~r/example2.com/, ~r/example.com/]
+  end
 end