streamline arm test names and get guard to pick up right tests

Guardfile

@@ -7,6 +7,9 @@ guard :minitest do
   watch(%r{^lib/(.*/)?([^/]+)\.rb$})     { |m| "test/#{m[1]}test_#{m[2]}.rb" }
   watch(%r{^test/test_helper\.rb$})      { 'test' }
 
+  #Arm instructions
+  watch(%r{^lib/arm/instructions/(.+)_instruction.rb}) { |m| "test/arm/test_#{m[1]}.rb" }
+
   # with Minitest::Spec
   # watch(%r{^spec/(.*)_spec\.rb$})
   # watch(%r{^lib/(.+)\.rb$})         { |m| "spec/#{m[1]}_spec.rb" }