使用Plug.Test无法发送JSON的问题咨询（附代码示例）

Let's break down why your test might be misbehaving and fix it step by step.

The Root Problem: Missing Content-Type Header #

Your test sends raw JSON data but doesn't set the Content-Type header to application/json. The Plug.Parsers with the :json parser only activates when it detects this specific header—without it, Plug won't parse the JSON body into conn.params, which is almost certainly causing issues in your handler logic.

Fix 1: Update Your Test to Include the Correct Header #

Modify your test to add the required header before calling your Plug. Here's the adjusted version:

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

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

Fix 2: Simplify with Plug.Conn.json/2 (Optional but Cleaner) #

You can skip manual JSON encoding and header setting entirely by using Plug.Conn.json/2, which handles both tasks for you:

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

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

Double-Check Your Plug's call Function #

Make sure your call function is complete and properly handles the request. A minimal working example would look like this:

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
    # Access parsed JSON data via conn.params here
    IO.inspect(conn.params, label: "Parsed Request Params")
    
    conn
    |> put_resp_content_type("application/json")
    |> send_resp(200, Jason.encode!(%{status: "success"}))
  end
end

Quick Verification #

After making these changes, run your test again. The Plug.Parsers should now correctly parse the JSON body into conn.params, and your Plug will handle the request as expected.

内容的提问来源于stack exchange，提问作者ngw