Make required by default test for belongs_to association clearer

Since #18937 `belongs_to` associations receive a setting to determine if
it should be or not treated as `required` by default.

While the tests were still passing, it was not evident that the
"default" behaviour for `required` could change in fuction of a setting,
that is set by default for fresh Rails5 apps, but not for upgraded
apps.

This commit try to relate them to make it clear what is the behaviour
expected when the setting is set as `true` or not set.

1 files changed, 25 insertions, 1 deletions

diff --git a/activerecord/test/cases/associations/required_test.rb b/activerecord/test/cases/associations/required_test.rb
index f8b686721e..0daa35ea83 100644
--- a/activerecord/test/cases/associations/required_test.rb
+++ b/activerecord/test/cases/associations/required_test.rb
@@ -22,7 +22,10 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
     @connection.drop_table "children", if_exists: true
   end
 
-  test "belongs_to associations are not required by default" do
+  test "belongs_to associations can be optional by default" do
+    original_value = ActiveRecord::Base.belongs_to_required_by_default
+    ActiveRecord::Base.belongs_to_required_by_default = false
+
     model = subclass_of(Child) do
       belongs_to :parent, inverse_of: false,
         class_name: "RequiredAssociationsTest::Parent"
@@ -30,6 +33,8 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
 
     assert model.new.save
     assert model.new(parent: Parent.new).save
+
+    ActiveRecord::Base.belongs_to_required_by_default = original_value
   end
 
   test "required belongs_to associations have presence validated" do
@@ -46,6 +51,25 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
     assert record.save
   end
 
+  test "belongs_to associations can be required by default" do
+    original_value = ActiveRecord::Base.belongs_to_required_by_default
+    ActiveRecord::Base.belongs_to_required_by_default = true
+
+    model = subclass_of(Child) do
+      belongs_to :parent, inverse_of: false,
+        class_name: "RequiredAssociationsTest::Parent"
+    end
+
+    record = model.new
+    assert_not record.save
+    assert_equal ["Parent must exist"], record.errors.full_messages
+
+    record.parent = Parent.new
+    assert record.save
+
+    ActiveRecord::Base.belongs_to_required_by_default = original_value
+  end
+
   test "has_one associations are not required by default" do
     model = subclass_of(Parent) do
       has_one :child, inverse_of: false,