Fix test failures caused by #19501

The first one is quite straightforward. We want to give the proper error
message in the case where a top level constant exists, but we're looking
for a nested one. We just need to port over the change to use
`subclass.name` into these changes.

The second set of failures, which are only present in the mysql adapter
tests, are stranger to me. The failure occurs because we were
previously comparing `subclass.name == self.name` instead of `subclass
== self`. However, I don't think that we need to support creating
anonymous classes which share a table with a class that uses STI,
overrides `name` to return the same name as athe class that we have no
other relationship with, when not assigned to a constant so it could
never be used anyway...

The commits around why that exist give no context, and I think they're
just poorly written tests (WTF does `test_schema` mean anyway, and why
does calling `.first` on some anonymous class test it?). We'll just
disable STI on that class.

3 files changed, 3 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index 53a9a9b797..741229f9c0 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -181,7 +181,7 @@ module ActiveRecord
             "or overwrite #{name}.inheritance_column to use another column for that information."
         end
         unless subclass == self || descendants.include?(subclass)
-          raise SubclassNotFound, "Invalid single-table inheritance type: #{type_name} is not a subclass of #{name}"
+          raise SubclassNotFound, "Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}"
         end
         subclass
       end
diff --git a/activerecord/test/cases/adapters/mysql/schema_test.rb b/activerecord/test/cases/adapters/mysql/schema_test.rb
index 2e18f609fd..a0f3c31e78 100644
--- a/activerecord/test/cases/adapters/mysql/schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql/schema_test.rb
@@ -14,6 +14,7 @@ module ActiveRecord
         @db_name    = db
 
         @omgpost = Class.new(ActiveRecord::Base) do
+          self.inheritance_column = :disabled
           self.table_name = "#{db}.#{table}"
           def self.name; 'Post'; end
         end
diff --git a/activerecord/test/cases/adapters/mysql2/schema_test.rb b/activerecord/test/cases/adapters/mysql2/schema_test.rb
index faf2acb9cb..1ebdca661c 100644
--- a/activerecord/test/cases/adapters/mysql2/schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/schema_test.rb
@@ -14,6 +14,7 @@ module ActiveRecord
         @db_name    = db
 
         @omgpost = Class.new(ActiveRecord::Base) do
+          self.inheritance_column = :disabled
           self.table_name = "#{db}.#{table}"
           def self.name; 'Post'; end
         end