README.md

# Bypass

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Bypass provides a quick way to create a custom plug that can be put in place instead of an actual
HTTP server to return prebaked responses to client requests. This is most useful in tests, when you
want to create a mock HTTP server and test how your HTTP client handles different types of
responses from the server.

## Installation

Add bypass to your list of dependencies in mix.exs:

```elixir
def deps do
  [{:bypass, "~> 0.1", only: :test}]
end
```

We do not recommended adding `:bypass` to the list of applications in your `mix.exs`. See below
for usage info.

Bypass supports Elixir 1.0 and up.


## Usage

Start Bypass in your `test/test_helper.exs` file to make it available in tests:

```elixir
ExUnit.start
Application.ensure_all_started(:bypass)
```

To use Bypass in a test case, open a connection and use its port to connect your client to it.

If you want to test what happens when the HTTP server goes down, use `Bypass.down/1` to close the
TCP socket and `Bypass.up/1` to start listening on the same port again. Both functions block until
the socket updates its state.

In the following example `TwitterClient.start_link()` takes the endpoint URL as its argument
allowing us to make sure it will connect to the running instance of Bypass.

```elixir
defmodule TwitterClientTest do
  use ExUnit.Case, async: true

  setup do
    bypass = Bypass.open
    {:ok, bypass: bypass}
  end

  test "client can handle an error response", %{bypass: bypass} do
    Bypass.expect bypass, fn conn ->
      assert "/1.1/statuses/update.json" == conn.request_path
      assert "POST" == conn.method
      Plug.Conn.resp(conn, 429, ~s<{"errors": [{"code": 88, "message": "Rate limit exceeded"}]}>)
    end
    {:ok, client} = TwitterClient.start_link(url: endpoint_url(bypass.port))
    assert {:error, :rate_limited} == TwitterClient.post_tweet(client, "Elixir is awesome!")
  end

  test "client can recover from server downtime", %{bypass: bypass} do
    Bypass.expect bypass, fn conn ->
      # We don't care about `request_path` or `method` for this test.
      Plug.Conn.resp(conn, 200, "")
    end
    {:ok, client} = TwitterClient.start_link(url: endpoint_url(bypass.port))

    assert :ok == TwitterClient.post_tweet(client, "Elixir is awesome!")

    # Blocks until the TCP socket is closed.
    Bypass.down(bypass)

    assert {:error, :noconnect} == TwitterClient.post_tweet(client, "Elixir is awesome!")

    Bypass.up(bypass)

    # When testing a real client that is using e.g. https://github.com/fishcakez/connection
    # with https://github.com/ferd/backoff to handle reconnecting, we'd have to loop for
    # a while until the client has reconnected.

    assert :ok == TwitterClient.post_tweet(client, "Elixir is awesome!")
  end

  defp endpoint_url(port), do: "http://localhost:#{port}/"
end
```

That's all you need to do. Bypass automatically sets up an `on_exit` hook to close its socket when
the test finishes running.

Multiple concurrent Bypass instances are supported, all will have a different unique port.

In case you need to assign a specific port to a Bypass instance to listen on, you can pass the
`port` option to `Bypass.open()`:

```elixir
bypass = Bypass.open(port: 1234)
```

## Configuration options

Set `:enable_debug_log` to `true` in the application environment to make Bypass log what it's doing:

```elixir
config :bypass, enable_debug_log: true
```

## License

This software is licensed under [the MIT license](LICENSE).