Fix regression in inverse_of on through associations

`inverse_of` on through associations was accidently removed/caused to
stop working in commit f8d2899 which was part of a refactoring on
`ThroughReflection`.

To fix we moved `inverse_of` and `check_validity_of_inverse!` to the
`AbstractReflection` so it's available to the `ThroughReflection`
without having to dup any methods. We then need to delegate `inverse_name`
method in `ThroughReflection`. `inverse_name` can't be moved to
`AbstractReflection` without moving methods that set the instance
variable `@automatic_inverse_of`.

This adds a test that ensures that `inverse_of` on a `ThroughReflection`
returns the correct class name, and the correct record for the inverse
relationship.

Fixes #21692

1 files changed, 13 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/inverse_associations_test.rb b/activerecord/test/cases/associations/inverse_associations_test.rb
index 423b8238b1..ece4dab539 100644
--- a/activerecord/test/cases/associations/inverse_associations_test.rb
+++ b/activerecord/test/cases/associations/inverse_associations_test.rb
@@ -13,6 +13,9 @@ require 'models/mixed_case_monkey'
 require 'models/admin'
 require 'models/admin/account'
 require 'models/admin/user'
+require 'models/developer'
+require 'models/company'
+require 'models/project'
 
 class AutomaticInverseFindingTests < ActiveRecord::TestCase
   fixtures :ratings, :comments, :cars
@@ -198,6 +201,16 @@ class InverseAssociationTests < ActiveRecord::TestCase
     belongs_to_ref = Sponsor.reflect_on_association(:sponsor_club)
     assert_nil belongs_to_ref.inverse_of
   end
+
+  def test_this_inverse_stuff
+    firm = Firm.create!(name: 'Adequate Holdings')
+    Project.create!(name: 'Project 1', firm: firm)
+    Developer.create!(name: 'Gorbypuff', firm: firm)
+
+    new_project = Project.last
+    assert Project.reflect_on_association(:lead_developer).inverse_of.present?, "Expected inverse of to be present"
+    assert new_project.lead_developer.present?, "Expected lead developer to be present on the project"
+  end
 end
 
 class InverseHasOneTests < ActiveRecord::TestCase