Raise exception instead of removed warn method.

lib/mactag/builder.rb

@@ -39,17 +39,15 @@ def has_gems?
     class << self
       def create
         unless gem_home_exists?
-          # EXCEPTION
-          Mactag.warn 'Gem home path does not exist on your system'
+          raise Mactag::MactagError.new("Specified gem home directory does not exist: #{Mactag::Config.gem_home}")
         end
 
-        if @builder.has_gems?
+        if builder.has_gems?
           Mactag::Ctags.new(@builder.files, Mactag::Config.tags_file).create
 
-          puts "Successfully generated TAGS file"
+          puts 'Successfully generated TAGS file'
         else
-          # EXCEPTION
-          Mactag.warn 'You did not specify anything to tag'
+          raise Mactag::MactagError.new('Nothing to tag')
         end
       end
 

spec/mactag/builder_spec.rb

@@ -106,9 +106,26 @@
     end
   end
 
+  describe '#create' do
+    it 'raises error when gem home does not exist' do
+      Mactag::Builder.stub(:gem_home_exists?) { false }
+      proc {
+        Mactag::Builder.create
+      }.should raise_exception(Mactag::MactagError)
+    end
+
+    it 'raises errors when gem home exists but there are no gems' do
+      Mactag::Builder.stub(:gem_home_exists?) { true }
+      Mactag::Builder.stub(:builder) { mock(:has_gems? => false) }
+      proc {
+        Mactag::Builder.create
+      }.should raise_exception(Mactag::MactagError)
+    end
+  end
+
   describe '#generate' do
     it 'accepts a block as argument' do
-      lambda {
+      proc {
         Mactag::Builder.generate {}
       }.should_not raise_exception
     end