Related: #19617, #19187, #19533, #19689, #19675.

'drb/unix' does not exist on mingw.

Preserving RACK_ENV behavior.

This reverts commit 7bdc7635, reversing
changes made to 45786be5.

Since the `ForkingExecutor` class seems to be pretty slow on Rubinius
due to DRb (c.f. http://git.io/xIVg), let's avoid running tests with
it on this platform.

Also, the `parallelize_me!` call make the suite to output a bunch of
errors due to rubinius/rubinius#2934 since there are thread-safety
problems with autoloading.

`_generate_paths_by_default` should always be private.

Fixes: https://github.com/rails/rails/issues/16814

Goals:

1. Default to :random for newly generated applications
2. Default to :sorted for existing applications with a warning
3. Only show the warning once
4. Only show the warning if the app actually uses AS::TestCase

Fixes #16769

We're seeing too many failures to believe otherwise.

This reverts commits bc116a55,
cbde413d,
bf0a6793, and
2440933f.

https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
added support and enabled parallel execution of the actionpack tests.

However it introduced https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
since one cannot connect to a socket file that's inside a Vagrant synced folder
due to security restrictions, and DRb tries to.

Also rename the temporary files to make it obvious that they're rails-related,
since now they're placed outside the project's directory.

Fixes https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364

UnexpectedError exceptions wrap the original exception, and the original
exception may contain a reference to something that can't be marshal
dumped which will cause the process to die.

Calling ActiveSupport::TestCase.i_suck_and_my_tests_are_order_dependent! in AS::TestCase makes
everyone's tests order dependent, which should never be done by the framework.

We are planning to remove mocha from our test suite because of
performance problems. To make this possible we should stop require mocha
on ActionSupport::TestCase.

This should not affect applications since users still need to add mocha
to Gemfile and this already load mocha.

Added FIXME notes to place that still need mocha removal

(I think)

this prevents the array from being dumped as a DRbObject so we can
reduce communication with the server.  the reporter should always exist
on the server side, so we don't have to worry about GC

only on forking systems though.  Feel free to revert this if it causes
problems.

this allows us to avoid 2 hash allocations per named helper definition,
also we can avoid a `merge` and `delete`.

Then we can avoid nil checks

This Adds helpers(jruby_skip & rbx_skip). In Future, Plan is to use
these helpers instead of calls directly to
RUBY_ENGINE/RbConfig/JRUBY_VERSION