test: e2e test for Extractive QA Pipeline (#5879)

* e2e test for e. qa pipeline

e2e/preview/pipelines/test_extractive_qa_pipeline.py

@@ -0,0 +1,53 @@
+from haystack.preview import Pipeline, Document
+from haystack.preview.document_stores import MemoryDocumentStore
+from haystack.preview.components.retrievers import MemoryBM25Retriever
+from haystack.preview.components.readers import ExtractiveReader
+
+
+def test_extractive_qa_pipeline():
+    document_store = MemoryDocumentStore()
+
+    documents = [
+        Document(text="My name is Jean and I live in Paris."),
+        Document(text="My name is Mark and I live in Berlin."),
+        Document(text="My name is Giorgio and I live in Rome."),
+    ]
+
+    document_store.write_documents(documents)
+
+    qa_pipeline = Pipeline()
+    qa_pipeline.add_component(instance=MemoryBM25Retriever(document_store=document_store), name="retriever")
+    qa_pipeline.add_component(instance=ExtractiveReader(model_name_or_path="deepset/tinyroberta-squad2"), name="reader")
+    qa_pipeline.connect("retriever", "reader")
+
+    questions = ["Who lives in Paris?", "Who lives in Berlin?", "Who lives in Rome?"]
+    answers_spywords = ["Jean", "Mark", "Giorgio"]
+
+    for question, spyword, doc in zip(questions, answers_spywords, documents):
+        result = qa_pipeline.run({"retriever": {"query": question}, "reader": {"query": question}})
+
+        extracted_answers = result["reader"]["answers"]
+
+        # we expect at least one real answer and no_answer
+        assert len(extracted_answers) > 1
+
+        # the best answer should contain the spyword
+        assert spyword in extracted_answers[0].data
+
+        # no_answer
+        assert extracted_answers[-1].data is None
+
+        # since these questions are easily answerable, the best answer should have higher probability than no_answer
+        assert extracted_answers[0].probability >= extracted_answers[-1].probability
+
+        for answer in extracted_answers:
+            assert answer.query == question
+
+            assert hasattr(answer, "probability")
+            assert hasattr(answer, "start")
+            assert hasattr(answer, "end")
+
+            assert hasattr(answer, "document")
+            # the answer is extracted from the correct document
+            if answer.document is not None:
+                assert answer.document == doc