Add jt test mri --fast

Author: eregon

test/mri/capi_tests.list

@@ -10,6 +10,7 @@ cext-ruby/bug_reporter/test_bug_reporter.rb
 cext-ruby/class/test_class2name.rb
 cext-ruby/debug/test_debug.rb
 cext-ruby/debug/test_profile_frames.rb
+cext-ruby/econv/test_append.rb
 cext-ruby/exception/test_data_error.rb
 cext-ruby/exception/test_enc_raise.rb
 cext-ruby/exception/test_ensured.rb

tool/jt.rb

@@ -820,10 +820,10 @@ def help
       MRI tests commands:
       jt test mri                                    run MRI tests
       #{MRI_TEST_MODULES.map { |k, h| format ' ' * 4 + '%-16s%s', k, h[:help] }.join("\n")}
-      jt test mri test/mri/tests/test_find.rb [-- <MRI runner options>]
+      jt test mri [--fast] test/mri/tests/test_find.rb [-- <MRI runner options>]
                                                      run tests in given file, -n option of the runner can be used to further
                                                      limit executed test methods
-        MRI_TEST_SUBPROCESSES=false                  skip MRI tests using subprocesses
+          --fast                                     skip MRI tests using subprocesses
       jt retag FILE                                  Remove MRI excludes and re-add as necessary for MRI tests
       ---
       jt test basictest                              run MRI's basictest suite
@@ -1279,6 +1279,10 @@ def test(*args)
       'MKMF_SET_EXTMK_TO_TRUE' => 'true',
     }
 
+    if extra_args.delete '--fast'
+      env_vars['MRI_TEST_SUBPROCESSES'] = 'false'
+    end
+
     cext_tests = test_files.select do |f|
       f.include?('cext-ruby') || MRI_TEST_CAPI_TESTS.include?(f)
     end