refactor: remove "exposed" @system_dir instance variable (in helper method)

[pvdb]

It is very unclear why the Rake::TestCase#rake_system_dir helper method:

defrake_system_dir@system_dir="system"FileUtils.mkdir_p@system_dirFile.writeFile.join(@system_dir,"sys1.rake"),<<~SYS task "sys1" do puts "SYS1" end SYSENV["RAKE_SYSTEM"]=@system_dirend

... creates and sets a @system_dir instance variable. 🤔

On inspection, it turns out its only use is the following assertion in one of the test cases:

assert_equal@system_dir,@app.system_dir

... so this PR removes the ivar and hardcodes the expected "system" value in the assertion:

- assert_equal @system_dir, @app.system_dir+ assert_equal "system", @app.system_dir

This may seem a tad controversial, but as it turns out, the sys1.rake Rakefile name and the SYS1 Rakefile contents (also "private" - as it were - to that very same utility method) are already hardcoded in one of the Rake test cases:

$ gitgrep -isys1 -- 'test/test*'test/test_rake_functional.rb: rake"-g","sys1"test/test_rake_functional.rb: assert_match %r{^SYS1},@outtest/test_rake_functional.rb: rake"-g","sys1","-T","extra"test/test_rake_functional.rb: rake"sys1","--trace"test/test_rake_functional.rb: assert_match %r{^SYS1},@outtest/test_rake_functional.rb: rake"-G","sys1"test/test_rake_functional.rb: rake"--nosearch","sys1"test/test_rake_functional.rb: assert_match %r{^SYS1},@out
$ _

... so the change in this PR just makes things more consistent with the other test cases and assertions.

[hsbt]

👍