(GH-57) Fix bug with i18n in the language server

The code use to do document validation was using the special function `_` which
was introduced in Puppet 4.9 for internationalisation.  This commit removes the
i18n function as it is not required for the language server itself and adds
some basic tests to prevent regression.

Author: glennsarti

server/lib/puppet-languageserver/document_validator.rb

@@ -45,7 +45,7 @@ def self.validate(content, _max_problems = 100)
       Puppet[:code] = content
       env = Puppet.lookup(:current_environment)
       loaders = Puppet::Pops::Loaders.new(env)
-      Puppet.override({ :loaders => loaders }, _('For puppet parser validate')) do
+      Puppet.override({ :loaders => loaders }, 'For puppet parser validate') do
         begin
           validation_environment = env
           validation_environment.check_for_reparse

server/spec/integration/puppet-languageserver/document_validator_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe 'document_validator' do
+  let(:subject) { PuppetLanguageServer::DocumentValidator }
+
+  describe '#validate' do
+    describe "Given an incomplete manifest which has syntax errors" do
+      let(:manifest) { 'user { "Bob"' }
+
+      it "should return at least one error" do
+        result = subject.validate(manifest)
+        expect(result.length).to be > 0
+      end
+    end
+
+    describe "Given a complete manifest with no validation errors" do
+      let(:manifest) { "user { 'Bob': ensure => 'present' }" }
+
+      it "should return an empty array" do
+        expect(subject.validate(manifest)).to eq([])
+      end
+    end
+
+  end
+end