diff --git a/README.md b/README.md
index 955771d..a4cafed 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,8 @@
 # Downstream
 
-
 [![Travis](https://img.shields.io/travis/mpiercy827/downstream.svg)](https://travis-ci.org/mpiercy827/downstream)
 [![Hex.pm](https://img.shields.io/hexpm/v/downstream.svg)](https://hex.pm/packages/downstream/)
 
-
 Downstream is a library for downloading files via HTTPoison response streaming.
 
 ## Installation
@@ -102,6 +100,7 @@ iex(2)> Downstream.get("https://www.google.com/notfound", file)
 iex(3)> File.close(file)
 :ok
 ```
+
 ## Current Features
 
 - Stream downloads via HTTP GET requests
@@ -143,3 +142,26 @@ any changes, run the following command:
 ```bash
 $ mix format
 ```
+
+### Testing
+
+HTTPoison can be swapped for a mock using configs.
+
+In test_helpers.exs
+
+```elixir
+Mox.defmock(AppName.MockHttp, for: HTTPoison.Base)
+Application.put_env(:downstream, :http_client, AppName.MockHttp)
+```
+
+In \*\_test.exs
+
+```elixir
+AppName.MockHttp
+|> expect(:get!, fn "http://localhost/test", [], [stream_to: pid] ->
+  send(pid, %HTTPoison.AsyncChunk{chunk: content})
+  send(pid, %HTTPoison.AsyncStatus{code: 200})
+  send(pid, %HTTPoison.AsyncHeaders{headers: []})
+  send(pid, %HTTPoison.AsyncEnd{})
+end)
+```
diff --git a/lib/downstream.ex b/lib/downstream.ex
index cdf487b..76c1fa8 100644
--- a/lib/downstream.ex
+++ b/lib/downstream.ex
@@ -28,7 +28,7 @@ defmodule Downstream do
     download_task = Task.async(Download, :stream, [io_device])
     httpoison_options = Keyword.merge(http_options, stream_to: download_task.pid)
 
-    HTTPoison.get!(url, headers, httpoison_options)
+    http_client().get!(url, headers, httpoison_options)
 
     try do
       Task.await(download_task, timeout)
@@ -67,7 +67,7 @@ defmodule Downstream do
 
     httpoison_options = Keyword.merge(http_options, stream_to: download_task.pid)
 
-    HTTPoison.post!(url, body, headers, httpoison_options)
+    http_client().post!(url, body, headers, httpoison_options)
 
     try do
       Task.await(download_task, timeout)
@@ -88,4 +88,8 @@ defmodule Downstream do
       {:error, %Error{reason: reason}} -> raise Error, reason: reason
     end
   end
+
+  def http_client() do
+    Application.get_env(:downstream, :http_client, HTTPoison)
+  end
 end