feat: make DocumentWriter return the actual number of documents wri…

…tten (#6366)

* make DocumentWriter return the actual number of documents written

* add/improve tests

haystack/preview/components/writers/document_writer.py

@@ -64,5 +64,5 @@ def run(self, documents: List[Document], policy: Optional[DuplicatePolicy] = Non
         if policy is None:
             policy = self.policy
 
-        self.document_store.write_documents(documents=documents, policy=policy)
-        return {"documents_written": len(documents)}
+        documents_written = self.document_store.write_documents(documents=documents, policy=policy)
+        return {"documents_written": documents_written}

test/preview/components/writers/test_document_writer.py

@@ -1,11 +1,10 @@
-from unittest.mock import MagicMock
-
 import pytest
 
 from haystack.preview import Document, DeserializationError
 from haystack.preview.testing.factory import document_store_class
 from haystack.preview.components.writers.document_writer import DocumentWriter
 from haystack.preview.document_stores import DuplicatePolicy
+from haystack.preview.document_stores.in_memory import InMemoryDocumentStore
 
 
 class TestDocumentWriter:
@@ -81,12 +80,27 @@ def test_from_dict_nonexisting_docstore(self):
 
     @pytest.mark.unit
     def test_run(self):
-        mocked_document_store = MagicMock()
-        writer = DocumentWriter(mocked_document_store)
+        document_store = InMemoryDocumentStore()
+        writer = DocumentWriter(document_store)
         documents = [
             Document(content="This is the text of a document."),
             Document(content="This is the text of another document."),
         ]
 
-        writer.run(documents=documents)
-        mocked_document_store.write_documents.assert_called_once_with(documents=documents, policy=DuplicatePolicy.FAIL)
+        result = writer.run(documents=documents)
+        assert result["documents_written"] == 2
+
+    @pytest.mark.unit
+    def test_run_skip_policy(self):
+        document_store = InMemoryDocumentStore()
+        writer = DocumentWriter(document_store, policy=DuplicatePolicy.SKIP)
+        documents = [
+            Document(content="This is the text of a document."),
+            Document(content="This is the text of another document."),
+        ]
+
+        result = writer.run(documents=documents)
+        assert result["documents_written"] == 2
+
+        result = writer.run(documents=documents)
+        assert result["documents_written"] == 0