docs: add example for a nil name in link_to

Fix Rails environment when running tests with Ruby

Option parsing happens too late to have any impact on the Rails
environment.  Rails accesses the environment name and memoizes it too
early in the boot process for a commandline option to have any impact on
the database connection, so we'll change this test to set the
environment from an environment variable (and ensure it still works when
running tests with `ruby`)

This reverts commit 9a80f525.

When tests are run with just `ruby`, the RAILS_ENV is set to
`development` too early, and we connect to the development database
rather than the test database.

`connection.primary_key` also return composite primary keys, so
`from_primary_key_column` may not be found even if `from_primary_key` is
presented.

```
% ARCONN=sqlite3 be ruby -w -Itest
test/cases/adapters/sqlite3/sqlite3_adapter_test.rb -n
test_copy_table_with_composite_primary_keys
Using sqlite3
Run options: -n test_copy_table_with_composite_primary_keys --seed 19041

# Running:

E

Error:
ActiveRecord::ConnectionAdapters::SQLite3AdapterTest#test_copy_table_with_composite_primary_keys:
NoMethodError: undefined method `type' for nil:NilClass
    /path/to/rails/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb:411:in
    `block in copy_table'
```

This change fixes `copy_table` to do not lose composite primary keys.

Fix issue #30658 by checking explicitly for 'null' referrer

Add headless firefox driver to System Tests

This regression was caused at 213796fb due to polymorphic predicates are
combined by `Arel::Nodes::And`. But I'd like to keep that combined
because it would help inverting polymorphic predicates correctly
(e9ba12f7), and we can collect equality nodes regardless of combined by
`Arel::Nodes::And` (`a AND (b AND c) AND d` == `a AND b AND c AND d`).
This change fixes the regression to collect equality nodes in
`Arel::Nodes::And` as well.

Fixes #31338.

Fix sqlite migrations with custom primary keys

[ci skip] Make `Todo` classes inherit `ApplicationRecord`

Example codes that use `has_many` or `before_create` in `Module::Concerning` look like active record models.
So I've made them inherit `ApplicationRecord`.

I frequently run tests with `ruby`, not with a runner like `rake` or
`rails`.  When running the test with just `ruby` the `RAILS_ENV`
environment variable did not get set to "test", and this would cause the
tests to fail (and even mutate the development database!)

This commit adds integration tests for running tests with just `ruby`
and ensures the environment gets defaulted to "test".  I also added a
test to ensure that passing an environment to `-e` actually works (and
fixed that case too).

An interesting / annoying thing is that Minitest picks up it's plugins
by asking RubyGems for a list of files:

  https://github.com/seattlerb/minitest/blob/ca6a71ca901016db09a5ad466b4adea4b52a504a/lib/minitest.rb#L92-L100

This means that RubyGems needs to somehow know about the file before it
can return it to Minitest.  Since we are not packaging Rails as a Gem
before running the integration tests on it (duh, why would you do
that?), RubyGems doesn't know about the file, so it can't tell Minitest,
so Minitest doesn't automatically require it.  This means I had to
manually require and insert the plugin in our integration test.  I've
left comments about that in the test as well.

Ugh.

Correct routing test spelling mistake.

Previously, if a record was created with a custom primary key, that
table could not be migrated using sqlite. While attempting to copy the
table, the type of the primary key was ignored.

Once that was corrected, copying the indexes would fail because custom
primary keys are autoindexed by sqlite by default.

To correct that, this skips copying the index if the index name begins
with "sqlite_". This is a reserved word that indicates that the
index is an internal schema object. SQLite prohibits applications from
creating objects whose names begin with "sqlite_", so this string should
be safe to use as a check.
ref https://www.sqlite.org/fileformat2.html#intschema

Use `:string` instead of `:text` for `JsonAttributeTest`

Address `ActiveRecord::NotNullViolation: OCIError: ORA-01400` for Oracle database which requires primary key value mentioned in insert statement explicitly.

Yield array from AC::Parameters#each for block with one arg

Matches Hash#each behaviour as used in Rails 4.

Add `assert_in_epsilon` to Testing guide [ci skip]

I found `assert_in_epsilon` is not be in "2.4 Available Assertions".
So I Added them.

MiniTest::Assertions#assert_in_epsilon:

https://github.com/seattlerb/minitest/blob/master/lib/minitest/assertions.rb#L204-L210

Since CLOB data type has many limitations in Oracle SELECT WHERE clause.

This reverts commit 23226d04, reversing
changes made to 7544cf76.

Execute `JsonAttributeTest` only if `supports_json?` returns `true`

Oracle enhanced adapter does not fully support JSON datatype then `supports_json?` returns `false`.
I wanted to skip known failures and errors when tested with Oracle enhanced adapter.

Speed up travis by only installing packages when needed

Add more tests for the `--webpack` option

These are needed when GEM=ast, thanks @georgeclaghorn

Follow up of 3c442b6d

Without this require, it will fail when run CSP test alone.
Ref: https://travis-ci.org/rails/rails/jobs/311715758#L2976

Fix example code in ActiveJob::Core [ci skip]

Use Object#deep_dup to safely duplicate policy values

1) It seems that it raise error on example code in `ActiveJob::Core`.

Before:

```ruby
class DeliverWebhookJob < ActiveJob::Base
  def serialize
    super.merge('attempt_number' => (@attempt_number || 0) + 1)
  end

  def deserialize(job_data)
    super
    @attempt_number = job_data['attempt_number']
  end

  rescue_from(Timeout::Error) do |exception|
    raise exception if @attempt_number > 5
    retry_job(wait: 10)
  end

  def perform
    raise Timeout::Error
  end
end
```

Then it run `DeliverWebhookJob.perform_now` in `rails console`. And raise error:

NoMethodError: undefined method `>' for nil:NilClass
from /app/jobs/deliver_webhook_job.rb:12:in `block in <class:DeliverWebhookJob>'

So I thought it's necessary to fix it.

After:

```ruby
class DeliverWebhookJob < ActiveJob::Base
  attr_writer :attempt_number

  def attempt_number
    @attempt_number ||= 0
  end

  def serialize
    super.merge('attempt_number' => attempt_number + 1)
  end

  def deserialize(job_data)
    super
    self.attempt_number = job_data['attempt_number']
  end

  rescue_from(Timeout::Error) do |exception|
    raise exception if attempt_number > 5
    retry_job(wait: 10)
  end

  def perform
    raise Timeout::Error
  end
end
```

Then it run `DeliverWebhookJob.perform_now` in `rails console`. And it does'nt raise error NoMethodError.

2) Use `Timeout::Error` instead of `TimeoutError` (`TimeoutError` is deprecated).

Add tests for the `--webpack` option