It is PRINCIPLES - truths; not PRINCIPALS - people in charge of schools or racing teams.

By deleteing the dev database, recreating it from migrations and then preparing the test database; the foreign key contraints now work. Also the database tables are now uft8mb4 instead of lantin1.

May be an idea to do this every time there is a rails update until going live.

test/fixtures/subprinciples.yml

@@ -1,11 +1,11 @@
 # Read about fixtures at https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
-
-one:
-  principle: one
-  name: MyString
-  description: MyText
-
-two:
-  principle: two
-  name: MyString
-  description: MyText
+#
+# one:
+#   principle: one
+#   name: MyString
+#   description: MyText
+#
+# two:
+#   principle: two
+#   name: MyString
+#   description: MyText