Field method refactor for Ead transform

Why these changes are being introduced:
* These updates are required to implement the architecture described
in the following ADR: https://github.com/MITLibraries/transmogrifier/blob/main/docs/adrs/0005-field-methods.md

How this addresses that need:
* Create field method for retrieving <archdesc> and <did> elements
  * Raise SkippedRecordEvent when either of <archdesc> or <did> is missing
* Update tests for Ead transform
  * Add new tests (success, blank, missing) for new field methods
  * Remove redundant tests

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/TIMX-287

tests/sources/xml/test_ead.py

@@ -4,6 +4,7 @@
 from bs4 import BeautifulSoup
 
 import transmogrifier.models as timdex
+from transmogrifier.exceptions import SkippedRecordEvent
 from transmogrifier.sources.xml.ead import Ead
 
 
@@ -266,32 +267,52 @@ def test_ead_record_all_fields_transform_correctly():
     )
 
 
-def test_ead_record_with_missing_archdesc_logs_error(caplog):
-    ead_xml_records = Ead.parse_source_file(
-        "tests/fixtures/ead/ead_record_missing_archdesc.xml"
+def test_ead_get_collection_description_success():
+    source_record = create_ead_source_record_stub(
+        metadata_insert=(
+            """
+            <archdesc level="collection">
+                <did>
+                </did>
+            </archdesc>
+            """
+        )
+    )
+    collection_description, collection_description_did = Ead.get_collection_description(
+        source_record
     )
-    output_records = Ead("aspace", ead_xml_records)
-    assert len(list(output_records)) == 0
-    assert output_records.processed_record_count == 1
     assert (
-        "transmogrifier.sources.xml.ead",
-        logging.ERROR,
-        "Record ID repositories/2/resources/4 is missing archdesc element",
-    ) in caplog.record_tuples
+        collection_description.name == "archdesc"
+        and collection_description["level"] == "collection"
+    )
+    assert collection_description_did.name == "did"
 
 
-def test_ead_record_with_missing_archdesc_did_logs_error(caplog):
-    ead_xml_records = Ead.parse_source_file(
-        "tests/fixtures/ead/ead_record_missing_archdesc_did.xml"
+def test_ead_get_collection_description_raises_skipped_record_event_if_archdesc_missing():
+    source_record = create_ead_source_record_stub()
+    with pytest.raises(
+        SkippedRecordEvent,
+        match=(
+            "Record skipped because key information is missing: "
+            '<archdesc level="collection">.'
+        ),
+    ):
+        Ead.get_collection_description(source_record)
+
+
+def test_ead_get_collection_description_raises_skipped_record_event_if_did_missing():
+    source_record = create_ead_source_record_stub(
+        metadata_insert=(
+            """
+            <archdesc level="collection"></archdesc>
+            """
+        )
     )
-    output_records = Ead("aspace", ead_xml_records)
-    assert len(list(output_records)) == 0
-    assert output_records.processed_record_count == 1
-    assert (
-        "transmogrifier.sources.xml.ead",
-        logging.ERROR,
-        "Record ID repositories/2/resources/3 is missing archdesc > did element",
-    ) in caplog.record_tuples
+    with pytest.raises(
+        SkippedRecordEvent,
+        match=("Record skipped because key information is missing: <did>"),
+    ):
+        Ead.get_collection_description(source_record)
 
 
 def test_ead_record_with_attribute_and_subfield_variations_transforms_correctly():

transmogrifier/sources/xml/ead.py

@@ -5,6 +5,7 @@
 
 import transmogrifier.models as timdex
 from transmogrifier.config import load_external_config
+from transmogrifier.exceptions import SkippedRecordEvent
 from transmogrifier.helpers import validate_date, validate_date_range
 from transmogrifier.sources.xmltransformer import XMLTransformer
 
@@ -18,36 +19,20 @@ class Ead(XMLTransformer):
     """EAD transformer."""
 
     def get_optional_fields(self, source_record: Tag) -> dict | None:
-        """
-        Retrieve optional TIMDEX fields from an EAD XML record.
-
-        Overrides metaclass get_optional_fields() method.
+        """_summary_
 
         Args:
-            xml: A BeautifulSoup Tag representing a single EAD XML record.
+            source_record (Tag): _description_
+
+        Returns:
+            dict | None: _description_
         """
         fields: dict = {}
 
         source_record_id = self.get_source_record_id(source_record)
-
-        if collection_description := source_record.metadata.find(
-            "archdesc", level="collection"
-        ):
-            pass
-        else:
-            message = f"Record ID {self.get_source_record_id(source_record)} is missing archdesc element"
-            logger.error(message)
-            return None
-
-        if collection_description_did := collection_description.did:
-            pass
-        else:
-            message = (
-                f"Record ID {self.get_source_record_id(source_record)} is missing archdesc > "
-                "did element"
-            )
-            logger.error(message)
-            return None
+        collection_description, collection_description_did = (
+            self.get_collection_description(source_record)
+        )
 
         control_access_elements = collection_description.find_all(
             "controlaccess", recursive=False
@@ -361,6 +346,23 @@ def generate_name_identifier_url(cls, name_element: Tag) -> list | None:
             return [base_url + identifier]
         return None
 
+    @classmethod
+    def get_collection_description(cls, source_record: Tag) -> tuple[Tag]:
+        if collection_description := source_record.metadata.find(
+            "archdesc", level="collection"
+        ):
+            if collection_description_did := collection_description.did:
+                return collection_description, collection_description_did
+            else:
+                message = "Record skipped because key information is missing: <did>."
+                raise SkippedRecordEvent(message)
+        else:
+            message = (
+                "Record skipped because key information is missing: "
+                '<archdesc level="collection">.'
+            )
+            raise SkippedRecordEvent(message)
+
     @classmethod
     def get_main_titles(cls, source_record: Tag) -> list[str]:
         """