Make this gem requireable

lib/protoboeuf.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+module Protoboeuf
+end

test/gem_test.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "helper"
+
+class GemTest < ProtoBoeuf::Test
+  def test_can_be_required
+    Tempfile.create do |file|
+      file.write(<<~RUBY)
+        require "bundler/inline"
+
+        gemfile do
+          gem "protoboeuf", path: "#{__dir__}/..", require: true
+        end
+
+        ::ProtoBoeuf
+
+        require "protoboeuf/codegen"
+
+        ::ProtoBoeuf::CodeGen
+
+        exit 0
+      RUBY
+
+      file.flush
+
+      assert(system(RbConfig.ruby, "-v", file.path), "Failed to require the gem")
+    end
+  end
+end