Run tests for `target/boxing.rb`.

target/boxing.rb

@@ -6,6 +6,8 @@ MRuby::Build.new('no_boxing') do |conf|
   toolchain :gcc
 
   conf.gembox 'default'
+  conf.enable_test
+  conf.enable_bintest
 end
 
 MRuby::Build.new('word_boxing') do |conf|
@@ -15,6 +17,8 @@ MRuby::Build.new('word_boxing') do |conf|
   conf.compilers.each do |c|
     c.defines += %w(MRB_WORD_BOXING)
   end
+  conf.enable_test
+  conf.enable_bintest
 end
 
 MRuby::Build.new('nan_boxing') do |conf|
@@ -24,5 +28,7 @@ MRuby::Build.new('nan_boxing') do |conf|
   conf.compilers.each do |c|
     c.defines += %w(MRB_NAN_BOXING)
   end
+  conf.enable_test
+  conf.enable_bintest
 end