无法使用Plug.Test

Question

我有这个简单的测试：

test "Welcomes Github" do
  json = Jason.encode!(%{repository: %{full_name: "test/test"}})
  conn =
    conn(:post, "/", json)
    |> Web.call([])

  assert conn.state == :sent
  assert conn.status == 200
end

接收此代码的代码是使用常见的Plug.Parsers解码Json的普通插件：

defmodule MrsNorris.Web do
  import Plug.Conn
  use Plug.Builder

  plug Plug.Parsers, parsers: [:json], pass: ["*/*"], json_decoder: Jason

  def init(options), do: options

  def call(conn, _opts) do
    conn
      |> super([])
      |> put_resp_content_type("text/plain")
      |> send_resp(200, "Welcome Github!\n")
  end
end

身体完全是空的（删除了一些不相关的数据）：

%Plug.Conn{
  adapter: {Plug.Adapters.Test.Conn, :...},
  assigns: %{},
  body_params: %{},
  cookies: %Plug.Conn.Unfetched{aspect: :cookies},
  host: "www.example.com",
  method: "POST",
  owner: #PID<0.306.0>,
  params: %{},
  path_params: %{},
  port: 80,
  query_params: %{},
  query_string: "",
  remote_ip: {127, 0, 0, 1},
  req_cookies: %Plug.Conn.Unfetched{aspect: :cookies},
  req_headers: [],
  request_path: "/",
  resp_cookies: %{},
  resp_headers: [{"cache-control", "max-age=0, private, must-revalidate"}],
  scheme: :http,
}

我做错了什么？