add file_extension validation for file_type

spec/factories/file_type.rb

@@ -186,6 +186,7 @@ FactoryBot.define do
   factory :makefile, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/makefile' }
+    file_extension { '' }
     executable
     indent_size { 2 }
     name { 'Makefile' }

spec/models/file_type_spec.rb

@@ -54,4 +54,10 @@ describe FileType do
   it 'validates the presence of a user' do
     expect(file_type.errors[:user]).to be_present
   end
+
+  it 'validates the presence of the file_extension' do
+    expect(file_type.errors[:file_extension]).to be_present
+    file_type.update(file_extension: '')
+    expect(file_type.errors[:file_extension]).to be_blank
+  end
 end