diff --git a/development_notebook/2024-03-20.md b/development_notebook/2024-03-20.md
new file mode 100644
index 0000000..d1ca8e0
--- /dev/null
+++ b/development_notebook/2024-03-20.md
@@ -0,0 +1,48 @@
+# State Of Work
+
+* Project has been fully configured from cookiecutter-django using MySQL.
+* Deployed to production at [negligentoctopus.pythonanywhere.com](negligentoctopus.pythonanywhere.com).
+
+Core models are being defined and added to the django-admin.
+Account and Transactions are implemented with balance as prefix-sum.
+
+## Update
+
+Testing for these model is being defined.
+
+# Today
+
+Testing required configuration of a db table 'test\_negligent\_octopus.
+This was achieved the same way as creating a normal table:
+- Go into sudo mysql
+- create table
+- grant all privileges to user
+After this pytest can create and drop the table as needed.
+
+Also, make sure that your app name is not relative, i.e., 'core' should be 'negligent\_octopus.core'.
+
+__To Continue__
+
+Factories are defined.
+Testing is currently defined as methods of a class.
+The function can receive arguments with the name of models, which will be created and passed automatically by pytest using the factories (if defined) or using fixtures (use @pytest.fixture).
+
+## Work Log
+__InProgress__
+* Add testing -- Functions are defined in class. Follow the one implemented as example.
+    * Test business logic
+        * Test balance is correct
+        * Test balance on account is safe for one, for many transaction, with or withput inital balance
+        * Test balance is same on change initial balance and change of a transaction
+        * Test that changing acc or timestamp fails
+
+__ToDo__
+
+__Done__
+* Configure testing environment
+* Factories for testing
+* Testing functions
+
+__Discarded__
+
+# To Do
diff --git a/negligent_octopus/core/apps.py b/negligent_octopus/core/apps.py
index c0ce093..0f7a089 100644
--- a/negligent_octopus/core/apps.py
+++ b/negligent_octopus/core/apps.py
@@ -2,5 +2,5 @@
 
 
 class CoreConfig(AppConfig):
-    default_auto_field = "django.db.models.BigAutoField"
-    name = "core"
+    name = "negligent_octopus.core"
+    verbose_name = "Core"
diff --git a/negligent_octopus/core/tests.py b/negligent_octopus/core/tests.py
deleted file mode 100644
index 7ce503c..0000000
--- a/negligent_octopus/core/tests.py
+++ /dev/null
@@ -1,3 +0,0 @@
-from django.test import TestCase
-
-# Create your tests here.
diff --git a/negligent_octopus/core/tests/__init__.py b/negligent_octopus/core/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/negligent_octopus/core/tests/factories.py b/negligent_octopus/core/tests/factories.py
new file mode 100644
index 0000000..5f6cb65
--- /dev/null
+++ b/negligent_octopus/core/tests/factories.py
@@ -0,0 +1,23 @@
+import factory
+from factory.django import DjangoModelFactory
+
+from negligent_octopus.core.models import Account
+from negligent_octopus.core.models import Transaction
+
+
+class AccountFactory(DjangoModelFactory):
+    class Meta:
+        model = Account
+
+    owner = factory.SubFactory("negligent_octopus.users.tests.factories.UserFactory")
+    name = factory.Faker("word")
+    initial_balance = factory.Faker("random_number", digits=2)
+
+
+class TransactionFactory(DjangoModelFactory):
+    class Meta:
+        model = Transaction
+
+    account = factory.SubFactory(AccountFactory)
+    amount = factory.Faker("random_number", digits=2)
+    title = factory.Faker("word")
diff --git a/negligent_octopus/core/tests/fixtures.py b/negligent_octopus/core/tests/fixtures.py
new file mode 100644
index 0000000..5b5890a
--- /dev/null
+++ b/negligent_octopus/core/tests/fixtures.py
@@ -0,0 +1,14 @@
+import pytest
+
+from negligent_octopus.core.tests.factories import AccountFactory
+from negligent_octopus.core.tests.factories import TransactionFactory
+
+
+@pytest.fixture()
+def account():
+    return AccountFactory()
+
+
+@pytest.fixture()
+def transaction():
+    return TransactionFactory()
diff --git a/negligent_octopus/core/tests/test_models.py b/negligent_octopus/core/tests/test_models.py
new file mode 100644
index 0000000..c1114bc
--- /dev/null
+++ b/negligent_octopus/core/tests/test_models.py
@@ -0,0 +1,37 @@
+import pytest
+from django.utils import timezone
+from faker import Faker
+
+from negligent_octopus.core.models import Account
+from negligent_octopus.core.tests.factories import TransactionFactory
+
+faker = Faker()
+
+
+@pytest.mark.django_db()
+class TestAccountTransactionBalance:
+    def test_account_balance(self, account: Account):
+        balance = account.initial_balance
+        for i in range(10):
+            balance += i
+            TransactionFactory(
+                account=account,
+                amount=i,
+                timestamp=timezone.now(),  # Make sure they are in order
+            )
+        assert account.balance == balance
+
+    def test_account_initial_balance_change(self, account: Account):
+        raise NotImplementedError
+
+    def test_transaction_added_last(self, account: Account):
+        raise NotImplementedError
+
+    def test_transaction_added_first(self, account: Account):
+        raise NotImplementedError
+
+    def test_transaction_added_middle(self, account: Account):
+        raise NotImplementedError
+
+    def test_transaction_change_amount(self, account: Account):
+        raise NotImplementedError