如何用RSpec验证POST请求的请求体？

方法一：Mock Net::HTTP#request 捕获请求对象做断言 #

通过Mock Net::HTTP 实例的 request 方法，捕获传入的请求对象，直接验证其请求体和Content-Type是否符合预期：

it "carries the expected request body with correct content type" do
  test_data = { id: 123 }
  expected_body = test_data.to_json

  # Mock Net::HTTP.new 返回一个带request方法的模拟实例
  http_mock = double("Net::HTTP")
  expect(Net::HTTP).to receive(:new).with("example.com", 443).and_return(http_mock)

  # 捕获request方法接收的请求对象，执行断言
  expect(http_mock).to receive(:request) do |request|
    expect(request.content_type).to eq("application/json")
    expect(request.body).to eq(expected_body)
    # 返回模拟响应，避免方法因无返回值报错
    double("response", code: "200", body: { success: true }.to_json)
  end

  Gateway.new.post_it(test_data)
end

方法二：用WebMock拦截并验证请求 #

WebMock可以直接拦截HTTP请求，无需手动Mock底层类，就能验证请求的URI、请求体、headers等所有细节：

1. 先在Gemfile的test组添加WebMock：

group :test do
  gem 'webmock'
end

2. 编写测试代码：

require 'webmock/rspec'

it "sends request to correct URI with expected body" do
  test_data = { id: 123 }
  expected_body = test_data.to_json

  # 拦截目标请求，设置验证规则和模拟响应
  stub_request(:post, "https://example.com/api")
    .with(
      body: expected_body,
      headers: { 'Content-Type' => 'application/json' }
    )
    .to_return(status: 200, body: { success: true }.to_json)

  Gateway.new.post_it(test_data)

  # 验证请求确实按规则被触发
  expect(WebMock).to have_requested(:post, "https://example.com/api")
    .with(body: expected_body, headers: { 'Content-Type' => 'application/json' })
end

这种方式比手动Mock更简洁，同时能覆盖完整的请求校验场景，无需依赖真实API服务。

内容的提问来源于stack exchange，提问作者Sig