In #225 it was reported that the output looks incorrect:

```
$ cat /tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb
def x.y.z
end
$ ruby /tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb
/tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb: --> /tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb
expected a delimiter to close the parametersunexpected '.', ignoring it
> 1  def x.y.z
> 2  end
```

Specifically:

```
expected a delimiter to close the parametersunexpected '.', ignoring it
```

However this does not show up when executing the debug executable:

```
$ bin/bundle exec exe/syntax_suggest /tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb
--> /tmp/4a71c7e417cc9eac0971e3a2519b295c/scratch.rb

expected a delimiter to close the parameters
unexpected '.', ignoring it

> 1  def x.y.z
> 2  end
```

This is because `exe/syntax_suggest` uses STDOUT.puts while calling `ruby` with the filename uses a fake IO object represented by MiniStringIO. This class was incorrectly not adding a newline to the end of the print.

The fix was to move the class to it's own file where it can be tested and then fix the behavior.

close https://github.com/ruby/syntax_suggest/pull/225

https://github.com/ruby/syntax_suggest/commit/d2ecd94a3b



Co-authored-by: Andy Yong <andyywz@gmail.com>