Define the stub in the migration even if they're only used in the test

Rails 7 can't find the associations when running the tests.  Resolves the test error:

Rails couldn't find a valid model for AddMissingEmsIdToSwitch::HostSwitch association. Please provide the :class_name option on the association declaration. If :class_name is already provided, make sure it's an ActiveRecord::Base subclass.

db/migrate/20190201173316_add_missing_ems_id_to_switch.rb

@@ -1,4 +1,32 @@
 class AddMissingEmsIdToSwitch < ActiveRecord::Migration[5.0]
+  class ExtManagementSystem < ActiveRecord::Base
+    self.inheritance_column = :_type_disabled
+  end
+
+  class Host < ActiveRecord::Base
+    self.inheritance_column = :_type_disabled
+
+    belongs_to :ext_management_system, :foreign_key => "ems_id", :class_name => "AddMissingEmsIdToSwitch::ExtManagementSystem"
+
+    has_many :host_switches, :class_name => "AddMissingEmsIdToSwitch::HostSwitch"
+    has_many :switches, :through => :host_switches, :class_name => "AddMissingEmsIdToSwitch::Switch"
+  end
+
+  class HostSwitch < ActiveRecord::Base
+    belongs_to :host, :class_name => "AddMissingEmsIdToSwitch::Host"
+    belongs_to :switch, :class_name => "AddMissingEmsIdToSwitch::Switch"
+  end
+
+  class Switch < ActiveRecord::Base
+    self.inheritance_column = :_type_disabled
+
+    belongs_to :ext_management_system, :foreign_key => "ems_id", :class_name => "AddMissingEmsIdToSwitch::ExtManagementSystem"
+    belongs_to :host, :class_name => "AddMissingEmsIdToSwitch::Host"
+
+    has_many :hosts, :through => :host_switches, :class_name => "AddMissingEmsIdToSwitch::Host"
+    has_many :host_switches, :class_name => "AddMissingEmsIdToSwitch::HostSwitch"
+  end
+
   def up
     say_with_time("Add missing ems_id to switch") do
       connection.execute <<-SQL

spec/migrations/20190201173316_add_missing_ems_id_to_switch_spec.rb

@@ -1,35 +1,5 @@
 require_migration
 
-class AddMissingEmsIdToSwitch < ActiveRecord::Migration[5.0]
-  class ExtManagementSystem < ActiveRecord::Base
-    self.inheritance_column = :_type_disabled
-  end
-
-  class Host < ActiveRecord::Base
-    self.inheritance_column = :_type_disabled
-
-    belongs_to :ext_management_system, :foreign_key => "ems_id", :class_name => "AddMissingEmsIdToSwitch::ExtManagementSystem"
-
-    has_many :host_switches, :class_name => "AddMissingEmsIdToSwitch::HostSwitch"
-    has_many :switches, :through => :host_switches, :class_name => "AddMissingEmsIdToSwitch::Switch"
-  end
-
-  class HostSwitch < ActiveRecord::Base
-    belongs_to :host, :class_name => "AddMissingEmsIdToSwitch::Host"
-    belongs_to :switch, :class_name => "AddMissingEmsIdToSwitch::Switch"
-  end
-
-  class Switch < ActiveRecord::Base
-    self.inheritance_column = :_type_disabled
-
-    belongs_to :ext_management_system, :foreign_key => "ems_id", :class_name => "AddMissingEmsIdToSwitch::ExtManagementSystem"
-    belongs_to :host, :class_name => "AddMissingEmsIdToSwitch::Host"
-
-    has_many :hosts, :through => :host_switches, :class_name => "AddMissingEmsIdToSwitch::Host"
-    has_many :host_switches, :class_name => "AddMissingEmsIdToSwitch::HostSwitch"
-  end
-end
-
 describe AddMissingEmsIdToSwitch do
   let(:switch_stub) { migration_stub(:Switch) }
   let(:host_stub) { migration_stub(:Host) }