testing_ruby.md: Update make test-all tips [ci skip]

[junaruga]

This PR is to update the document about testing Ruby.

I think to explain the specific test case, the complete matching --name=TestingClass#test_method is better than the regular expression matching --name=/something/.

And I think the following command is helpful to know the options.

$ make test-all TESTS=--help

It is explained in the common.mk with the TESTOPTS="--help". However, as I see that the TESTS is only used in the test-all section in the testing_ruby.md, I am using TESTS=--help to align other parts.

The modified document is [https://github.com/junaruga/ruby/blob/wip/doc-contributing/doc/contributing/testing_ruby.md].

Debugging the specific test with debug gem

By the way, I wanted to add the way to debug a test with debug gem in the make test-all in the testing_ruby.md. I see it's useful to debug.

$ ./configure

$ make

$ make test-all TESTS="test/ruby/test_alias.rb --name=TestAlias#test_alias_with_zsuper_method" RUN_OPTS=-rdebug/start
[1, 10] in ./test/runner.rb
     1| # frozen_string_literal: true
     2| 
     3| # Should be done in rubygems test files?
=>   4| ENV["GEM_SKIP"] = "".freeze
     5| ENV.delete("RUBY_CODESIGN")
     6| 
     7| Warning[:experimental] = false
     8| 
     9| gem_path = [
    10|   File.realdirpath(".bundle"),
=>#0	<main> at ./test/runner.rb:4
(rdbg) b TestAlias#test_alias_with_zsuper_method    # break command
Unknown constant name: "TestAlias"
#0  BP - Method (pending)  TestAlias#test_alias_with_zsuper_method
(rdbg) c    # continue command
Run options: 
  --seed=9328
  "--ruby=./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- -rdebug/start"
  --excludes-dir=./test/excludes
  --name=!/memory_leak/
  --name=TestAlias#test_alias_with_zsuper_method

# Running tests:

[1/0] TestAlias#test_alias_with_zsuper_method[96, 105] in ~/var/git/ruby/ruby/test/ruby/test_alias.rb
    96|       end
    97|     end
    98|   end
    99| 
   100|   def test_alias_with_zsuper_method
=> 101|     c = Class.new
   102|     c.class_eval do
   103|       def foo
   104|         :ok
   105|       end
=>#0	TestAlias#test_alias_with_zsuper_method at ~/var/git/ruby/ruby/test/ruby/test_alias.rb:101
  #1	Test::Unit::TestCase#run_test(name=:test_alias_with_zsuper_method) at ~/var/git/ruby/ruby/tool/lib/test/unit/testcase.rb:200
  # and 24 frames (use `bt' command for all frames)

Stop by #0  BP - Method  TestAlias#test_alias_with_zsuper_method at /home/jaruga/var/git/ruby/ruby/test/ruby/test_alias.rb:100
(rdbg) 

However, maybe this document is written as a prerequisite where the current working directory is in the build directory that is written in the building_ruby.md. In the case, I couldn't run the specific unit test with debug gem. So, I couldn't write this way to the document.

$ mkdir build && cd build

$ ../configure --prefix="${HOME}/.rubies/ruby-master"

$ make

$ make test-all TESTS="../test/ruby/test_alias.rb --name=TestAlias#test_alias_with_zsuper_method" RUN_OPTS=-rdebug/start
../revision.h updated
generating x86_64-linux-fake.rb
x86_64-linux-fake.rb updated
<internal:/home/jaruga/var/git/ruby/ruby2/lib/rubygems/core_ext/kernel_require.rb>:85:in `require': cannot load such file -- debug/start (LoadError)
	from <internal:/home/jaruga/var/git/ruby/ruby2/lib/rubygems/core_ext/kernel_require.rb>:85:in `require'
make: *** [uncommon.mk:831: yes-test-all] Error 1

[nobu]

Also ruby test/runner.rb --help can, if your ruby is 2.7 or later.

[junaruga]

Thanks for the info. Do you have an idea about how to add the ruby test/runner.rb --help to this document?

Like this? Or you just introduced the way here. And you think we don't need to add the ruby test/runner.rb --help to the document? I suppose that adding the runtime ruby version requires 2.7 or later is a bit too detailed.

diff --git a/doc/contributing/testing_ruby.md b/doc/contributing/testing_ruby.md
index 167ab55c55..1289cd4341 100644
--- a/doc/contributing/testing_ruby.md
+++ b/doc/contributing/testing_ruby.md
@@ -85,6 +85,12 @@ We can run any of the make scripts [in parallel](building_ruby.md#label-Running+
     $ make test-all TESTS=--help
     ```
 
+    We can also display the help with
+
+    ```
+    $ ruby test/runner.rb --help
+    ```
+
     If we would like to run both the `test/` and `bootstraptest/` test suites, we can run
 
     ```

[junaruga]

I checked who created and updated the document file by git log doc/contributing/testing_ruby.md. It was created at c00feff.

Jemma Issroff (@jemmaissroff), Peter Zhu (@peterzhu2118) and Stan Lo (@st0012), what do you think about this PR?

[peterzhu2118]

Looks good, thanks!

[junaruga]

Thanks for your review!