Verify that route constraints respond to the expected messages instead of silently failing to enforce the constraint
Refactor AR's validations_test.rb

The `:context` switch feature is implemented in
ActiveRecord::Validations#valid? method, so we should rename the test
names, and execute `valid?` in the test.

Change test name in AR's validations_test.rb

This test is testing save method's code
Fix bugs with changed attributes tracking when transaction gets rollback
Fix Hash#deep_merge bug and improve documentation — resolves #12738

Previously merging into a hash with a falsy value would not result in
the merge-block being called. The fix is simply to check for presence
of the key in the hash.

The documentation example for `deep_merge` now appropriately
demonstrates what a deep merge does.
Fix exception when logging SQL w/ nil binary value.
make `db:structure:load` listed with `rake -T`
[Fixes #14948] Hash#to_query: Changed a way how empty hash and empty array are serialized

Empty Hash or Array should not present in serialization result

    {a: []}.to_query # => ""
    {a: {}}.to_query # => ""

For more info see #14948.
Typo, grammar and textual changes [ci skip]
docs, restructure newly added part to `includes`. [ci skip]

This is a follow up to #14139.

/cc @carlosantoniodasilva
Merge pull request #14952 from gregmolnar/schema_load

make `db:structure:load` listed with `rake -T`
Refactor test to not care about the specific result of valid?

Only care about its truthiness rather than asserting specific true/false
values. If we need to check for the return value in particular, there will
be a test for that.
Remove duplicated fixture addition
Reorganize ActiveRecord tasks [Arun Agrawal & Abd ar-Rahman Hamidi]
Merge pull request #14940 from arunagw/hbakhtiyor-test-db-namespaces-ar

Reorganize ActiveRecord's rake tasks
Revert "Merge pull request #14940 from arunagw/hbakhtiyor-test-db-namespaces-ar"

This reverts commit fe9859600824268ff614cb3eb48b62c7165a1fbd, reversing
changes made to add9560643ef79830febf47fa1228752d1df3502.
Fix Formatting in AR Readme

Don't make free form text appear in code blocks [ci skip]
Remove tests method for test cases when controller can be inferred.
Merge pull request #14959 from akshay-vishnoi/doc_changes

Typo, grammar and textual changes [ci skip]
Merge pull request #14966 from tgxworld/remove_unnecessary_setting_of_controller_name

Remove tests method for test cases when controller can be inferred.
refactor, move `column_for` to `AbstractAdapter` for better reuse.