Test server.rb with better isolation (#585)

* Test `server.rb` with better isolation

* Ensure sorbet not loaded

* Explain shim

* Explain the separate Rake tasks

Author: Andy Waite

Rakefile

@@ -10,10 +10,19 @@ load "rails/tasks/statistics.rake"
 require "bundler/gem_tasks"
 require "rake/testtask"
 
+# Since `server.rb` runs within the host Rails application, we want to ensure
+# we don't accidentally depend on sorbet-runtime. `server_test` intentionally doesn't use `test_helper`.
+# We run `server_test` in a seperate Rake task.
 Rake::TestTask.new(:test) do |t|
   t.libs << "test"
   t.libs << "lib"
-  t.test_files = FileList["test/**/*_test.rb"]
+  t.test_files = FileList["test/**/*_test.rb"] - ["test/ruby_lsp_rails/server_test.rb"]
 end
 
-task default: [:"db:setup", :test]
+Rake::TestTask.new(:server_test) do |t|
+  t.libs << "test"
+  t.libs << "lib"
+  t.test_files = ["test/ruby_lsp_rails/server_test.rb"]
+end
+
+task default: [:"db:setup", :test, :server_test]

sorbet/rbi/shims/server_test.rbi

@@ -0,0 +1,11 @@
+# typed: strict
+# frozen_string_literal: true
+
+module RubyLsp
+  module Rails
+    class Server
+      # We need this since RBS doesn't yet have a replacement for T.unsafe()
+      def print_it!; end
+    end
+  end
+end

test/ruby_lsp_rails/server_test.rb

@@ -1,9 +1,20 @@
 # typed: true
 # frozen_string_literal: true
 
-require "test_helper"
+# Configure Rails Environment
+ENV["RAILS_ENV"] = "test"
+require_relative "../dummy/config/environment"
+
+require "minitest/autorun"
+require "mocha/minitest"
 require "ruby_lsp/ruby_lsp_rails/server"
 
+if defined?(T)
+  puts "T is defined, indicating that sorbet-runtime was loaded"
+  puts "This test should run without sorbet-runtime"
+  exit(1)
+end
+
 class ServerTest < ActiveSupport::TestCase
   setup do
     @stdout = StringIO.new
@@ -246,7 +257,7 @@ def print_it!
       end
     end
 
-    T.unsafe(server).print_it!
+    server.print_it!
 
     assert_match("Content-Length: 70\r\n\r\n", stderr.string)
     assert_match(