diff --git a/src/documents/serialisers.py b/src/documents/serialisers.py
index bb16ce826..49a429e8f 100644
--- a/src/documents/serialisers.py
+++ b/src/documents/serialisers.py
@@ -412,21 +412,15 @@ class CustomFieldSerializer(serializers.ModelSerializer):
         ]
 
 
-class CustomFieldOnUpdateSerializer(serializers.ModelSerializer):
-    id = serializers.PrimaryKeyRelatedField(queryset=CustomField.objects.all())
-
-    class Meta:
-        model = CustomField
-        fields = [
-            "id",
-        ]
-
-
 class ReadWriteSerializerMethodField(serializers.SerializerMethodField):
-    def __init__(self, method_name=None, **kwargs):
+    """
+    Based on https://stackoverflow.com/a/62579804
+    """
+
+    def __init__(self, method_name=None, *args, **kwargs):
         self.method_name = method_name
         kwargs["source"] = "*"
-        super(serializers.SerializerMethodField, self).__init__(**kwargs)
+        super(serializers.SerializerMethodField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, data):
         return {self.field_name: data}
@@ -437,7 +431,7 @@ class CustomFieldInstanceSerializer(serializers.ModelSerializer):
     value = ReadWriteSerializerMethodField()
 
     def create(self, validated_data):
-        type_to_key_map = {
+        type_to_data_store_name_map = {
             CustomField.FieldDataType.STRING: "value_text",
             CustomField.FieldDataType.URL: "value_url",
             CustomField.FieldDataType.DATE: "value_date",
@@ -449,13 +443,14 @@ class CustomFieldInstanceSerializer(serializers.ModelSerializer):
         # And to a CustomField
         custom_field: CustomField = validated_data["field"]
         # This key must exist, as it is validated
-        expected_key = type_to_key_map[custom_field.data_type]
+        data_store_name = type_to_data_store_name_map[custom_field.data_type]
 
         # Actually update or create the instance, providing the value
+        # to fill in the correct attribute based on the type
         instance, _ = CustomFieldInstance.objects.update_or_create(
             document=document,
             field=custom_field,
-            defaults={expected_key: validated_data["value"]},
+            defaults={data_store_name: validated_data["value"]},
         )
         return instance
 
diff --git a/src/documents/tests/test_api_custom_fields.py b/src/documents/tests/test_api_custom_fields.py
index c80e75cda..7d21f1ffe 100644
--- a/src/documents/tests/test_api_custom_fields.py
+++ b/src/documents/tests/test_api_custom_fields.py
@@ -1,5 +1,4 @@
 from datetime import date
-from pprint import pprint
 
 from django.contrib.auth.models import User
 from rest_framework import status
@@ -52,6 +51,16 @@ class TestCustomField(DirectoriesMixin, APITestCase):
             self.assertEqual(data["data_type"], field_type)
 
     def test_create_custom_field_instance(self):
+        """
+        GIVEN:
+            - Field of each data type is created
+        WHEN:
+            - API request to create custom metadata instance with each data type
+        THEN:
+            - the field instance is created
+            - the field returns the correct fields and values
+            - the field is attached to the given document
+        """
         doc = Document.objects.create(
             title="WOW",
             content="the content",
@@ -127,10 +136,17 @@ class TestCustomField(DirectoriesMixin, APITestCase):
 
         doc.refresh_from_db()
         self.assertEqual(len(doc.custom_fields.all()), 5)
-        for custom_field in doc.custom_fields.all():
-            print(custom_field.value, type(custom_field.value))
 
     def test_change_custom_field_instance_value(self):
+        """
+        GIVEN:
+            - Custom field instance is created and attached to document
+        WHEN:
+            - API request to create change the value of the custom field
+        THEN:
+            - the field instance is updated
+            - the field returns the correct fields and values
+        """
         doc = Document.objects.create(
             title="WOW",
             content="the content",
@@ -144,6 +160,7 @@ class TestCustomField(DirectoriesMixin, APITestCase):
 
         self.assertEqual(CustomFieldInstance.objects.count(), 0)
 
+        # Create
         resp = self.client.patch(
             f"/api/documents/{doc.id}/",
             data={
@@ -158,12 +175,10 @@ class TestCustomField(DirectoriesMixin, APITestCase):
         )
 
         self.assertEqual(resp.status_code, status.HTTP_200_OK)
-
-        pprint(resp.json())
-
-        self.assertEqual(doc.custom_fields.first().value, "test value")
         self.assertEqual(CustomFieldInstance.objects.count(), 1)
+        self.assertEqual(doc.custom_fields.first().value, "test value")
 
+        # Update
         resp = self.client.patch(
             f"/api/documents/{doc.id}/",
             data={
@@ -177,13 +192,20 @@ class TestCustomField(DirectoriesMixin, APITestCase):
             format="json",
         )
         self.assertEqual(resp.status_code, status.HTTP_200_OK)
-
-        pprint(resp.json())
-
-        self.assertEqual(doc.custom_fields.first().value, "a new test value")
         self.assertEqual(CustomFieldInstance.objects.count(), 1)
+        self.assertEqual(doc.custom_fields.first().value, "a new test value")
 
     def test_delete_custom_field_instance(self):
+        """
+        GIVEN:
+            - Multiple custom field instances are created and attached to document
+        WHEN:
+            - API request to remove a field
+        THEN:
+            - the field instance is removed
+            - the other field remains unchanged
+            - the field returns the correct fields and values
+        """
         doc = Document.objects.create(
             title="WOW",
             content="the content",
@@ -240,6 +262,17 @@ class TestCustomField(DirectoriesMixin, APITestCase):
         self.assertEqual(doc.custom_fields.first().value, date_value)
 
     def test_custom_field_validation(self):
+        """
+        GIVEN:
+            - Document exists with no fields
+        WHEN:
+            - API request to remove a field
+            - API request is not valid
+        THEN:
+            - HTTP 400 is returned
+            - No field created
+            - No field attached to the document
+        """
         doc = Document.objects.create(
             title="WOW",
             content="the content",
@@ -258,7 +291,7 @@ class TestCustomField(DirectoriesMixin, APITestCase):
                     {
                         "field": custom_field_string.id,
                         # Whoops, spelling
-                        "value_test": "a new test value",
+                        "valeu": "a new test value",
                     },
                 ],
             },