It appears that as of version 4 the `db:test:prepare` task no longer depends on the `abort_if_pending_migrations` task, which leaves this comment out of sync.

These new methods are used from the Active Record model layer to
determine which relations are viable to back a model. These new methods
allow us to change `conn.tables` in the future to only return tables and
no views. Same for `conn.table_exists?`.

The goal is to provide the following introspection methods on the
connection:

* `tables`
* `table_exists?`
* `views`
* `view_exists?`
* `data_sources` (views + tables)
* `data_source_exists?` (views + tables)

Many user look `desc` of rake task and they are not familiar with `AR`.
`Active Record` is more familiar word.

Closes #20743.

The task `db:_dump` now only dumps the schema if
`ActiveRecord::Base.dump_schema_after_migration` is true. This has
effects:

- `db:migrate:up`
- `db:migrate:down`
- `db:forward`
- `db:rollback`

revert create and drop task descriptions

db:reset should not prematurely load the environment, so, for instance,
if there is any initializer that touches th DB, it will not touch that
before droping it.

Also this makes the code simpler.

This changed was made back in 15fb4302
, not sure why. But I am pretty much sure we should do it like this, as
drop and setup should load its dependencies tasks if necessary.

This reverts commit 08ff4ccb, reversing
changes made to 6c9ed6db.

Caused by #17920.

Closes #19545.

This patch introduced regressions because initializers were no longer
loaded. Specifically missing inflections result in broken restores of
the database.

`rake test:load_structure` already uses `SCHEMA` and there's no
need to maintain two different env vars.

All of the behavior :environment was giving (that db:schema:load needed)
was provided as well with :load_config.

This will address an issue introduced in
https://github.com/rails/rails/pull/15394. The fact that db:schema:load
now drops and creates the database causes the Octopus gem to have [an
issue](https://github.com/tchandy/octopus/issues/273) during the drop
step for the test database (which wasn't happening in db:schema:load
before). The error looks like:

    ActiveRecord::StatementInvalid: PG::ObjectInUse: ERROR:  cannot drop the currently open database
    : DROP DATABASE IF EXISTS "app_test"

Because of the timing, this issue is present in master, 4-2-*, and
4.1.8.

A note to forlorn developers who might see this: "Additionally" in a
commit message means you should have a separate commit, with a separate
justification for changes. Small commits with big messages are your
friends.

This reverts deprecations added in #13528.
The task is brought back for two reasons:
  1. Give plugins a way to hook into the test database initialization process
  2. Give the user a way to force a test database synchronization

While `test:prepare` is still a dependency of every test task, `db:test:prepare`
no longer hooks into it. This means that `test:prepare` runs before the schema
is synchronized. Plugins, which insert data can now hook into `db:test:prepare`.

The automatic schema maintenance can't detect when a migration is rolled-back,
modified and reapplied. In this case the user has to fall back to `db:test:prepare`
to force the synchronization to happen.

This reverts commit 482fdad5.

Fixes #17237.

Hash#keys.each allocates an array of keys; Hash#each_key iterates through the
keys without allocating a new array. This is the reason why Hash#each_key
exists.

The rake tasks and the `DatabaseTakss` adapter classes used to
assume a configuration at some places. This forced the rake
tasks to establish a specific connection before calling into
`load_schema`.

After #15394 this started to cause issues because it could
`purge` the wrong database before loading the schema.

This extracts the logic that was embedded in a Rake task into a static
method.
Bonus: the first test for `rake db:migrate`

It allows the code to be more declarative and elegant.

`ActiveRecord::FixtureSet.create_fixtures` can accept an array of
fixture_files.

Before this commit, if `ENV['FIXTURES_PATH']` was set, then `Rails.root`
was used, otherwise the app used `ActiveRecord::Tasks::DatabaseTasks.root`.

Now it is consistent.

The migration numbers were normalized different ways. This left
the task output in an inconsistent state.

Closes #15538.

This PR fixes #8930 and some stuff from #8985