Make sure did_you_mean feature works when the gem is available

Gemfile

@@ -33,6 +33,9 @@ group :test do
   else
     gem "webmock"
   end
+  if RUBY_VERSION >= '2.5.0'
+    gem 'did_you_mean'
+  end
 end
 
 gemspec

lib/thor/error.rb

@@ -3,16 +3,14 @@ class Thor
     begin
       require 'did_you_mean'
 
-      module DidYouMean
-        # In order to support versions of Ruby that don't have keyword
-        # arguments, we need our own spell checker class that doesn't take key
-        # words. Even though this code wouldn't be hit because of the check
-        # above, it's still necessary because the interpreter would otherwise be
-        # unable to parse the file.
-        class NoKwargSpellChecker < SpellChecker
-          def initialize(dictionary)
-            @dictionary = dictionary
-          end
+      # In order to support versions of Ruby that don't have keyword
+      # arguments, we need our own spell checker class that doesn't take key
+      # words. Even though this code wouldn't be hit because of the check
+      # above, it's still necessary because the interpreter would otherwise be
+      # unable to parse the file.
+      class NoKwargSpellChecker < DidYouMean::SpellChecker # :nodoc:
+        def initialize(dictionary)
+          @dictionary = dictionary
         end
       end
 
@@ -43,7 +41,7 @@ def corrections
       end
 
       def spell_checker
-        DidYouMean::NoKwargSpellChecker.new(error.all_commands)
+        NoKwargSpellChecker.new(error.all_commands)
       end
     end
 
@@ -85,8 +83,7 @@ def corrections
       end
 
       def spell_checker
-        @spell_checker ||=
-          DidYouMean::NoKwargSpellChecker.new(error.switches)
+        @spell_checker ||= NoKwargSpellChecker.new(error.switches)
       end
     end
 

spec/base_spec.rb

@@ -264,7 +264,7 @@ def hello
 
     it "suggests commands that are similar if there is a typo" do
       expected = "Could not find command \"paintz\" in \"barn\" namespace.\n"
-      expected << "Did you mean?  \"paint\"" if Thor::Correctable
+      expected << "Did you mean?  \"paint\"\n" if Thor::Correctable
 
       expect(capture(:stderr) { Barn.start(%w(paintz)) }).to eq(expected)
     end