Unit testing rack middlewares

middleware.rb

# Make sure rack & rspec are installed -> gem install rack rspec
# Run this script using rspec -> rspec middleware.rb

require 'rack'

class BlockActions
  def initialize(app)
    @app = app
  end

  def call(env)
    unless env["HTTP_X_CLIENT"] == "mobile" && env["HTTP_X_MOBILE_USER_ID"]
      return [
        400, # status
        { "Content-Type" => "application/json" }, # headers
        ["Invalid Request"] # response body
      ]
    end
    @app.call(env)
  end
end

require 'rspec'

describe BlockActions do
  # Mock env to pass in middleware
  let(:env) { Rack::MockRequest.env_for }

  # dummy app to validate success
  let(:app) { ->(env) { [200, {}, "success"] } }

  subject { BlockActions.new(app) }

  it "allows if client & user-id headers are present" do
    env["HTTP_X_CLIENT"] = "mobile"
    env["HTTP_X_MOBILE_USER_ID"] = 1
    status, _headers, _response = subject.call(env)
    expect(status).to eq(200)
  end

  it "does not allow if client is missing" do
    env["HTTP_X_MOBILE_USER_ID"] = 1
    status, _headers, _response = subject.call(env)
    expect(status).to eq(400)
  end

  it "does not allow if mobile-user-id is missing" do
    env["HTTP_X_CLIENT"] = "mobile"
    status, _headers, _response = subject.call(env)
    expect(status).to eq(400)
  end

  it "does not allow if client is not mobile" do
    env["HTTP_X_CLIENT"] = "jared"
    status, _headers, _response = subject.call(env)
    expect(status).to eq(400)
  end
end