test: add synthesizer deterministic contract tests

tests/unit/test_synthesizer.py

@@ -0,0 +1,93 @@
+from __future__ import annotations
+
+import pytest
+
+from anchor.synthesizer import Synthesizer
+
+
+def _spy_model(response: str = "synthesized answer"):
+    """Returns (model_fn, calls). Each call appends the user-role prompt text."""
+    calls: list[str] = []
+
+    def model_fn(messages: list[dict]) -> str:
+        calls.append(messages[0]["content"])
+        return response
+
+    return model_fn, calls
+
+
+@pytest.mark.unit
+def test_empty_chunks_returns_fallback_without_calling_model() -> None:
+    model_fn, calls = _spy_model()
+    result = Synthesizer(model_fn).synthesize([])
+    assert result == "No relevant information found in memory."
+    assert calls == []
+
+
+@pytest.mark.unit
+def test_single_chunk_returns_formatted_content_without_calling_model() -> None:
+    model_fn, calls = _spy_model()
+    chunk = {"source": "doc_A", "content": "The sky is blue."}
+    result = Synthesizer(model_fn).synthesize([chunk])
+    assert result == "[Source: doc_A]\nThe sky is blue."
+    assert calls == []
+
+
+@pytest.mark.unit
+def test_multi_chunk_with_questions_prompt_contains_chunk_content_and_sources() -> None:
+    model_fn, calls = _spy_model()
+    chunks = [
+        {"source": "src_1", "content": "fact one"},
+        {"source": "src_2", "content": "fact two"},
+    ]
+    Synthesizer(model_fn).synthesize(chunks, questions=["What is X?"])
+    assert len(calls) == 1
+    prompt = calls[0]
+    assert "fact one" in prompt
+    assert "fact two" in prompt
+    assert "[Source: src_1]" in prompt
+    assert "[Source: src_2]" in prompt
+
+
+@pytest.mark.unit
+def test_multi_chunk_with_single_question_marks_it_current() -> None:
+    model_fn, calls = _spy_model()
+    chunks = [
+        {"source": "s1", "content": "alpha"},
+        {"source": "s2", "content": "beta"},
+    ]
+    Synthesizer(model_fn).synthesize(chunks, questions=["Tell me about alpha"])
+    assert "Tell me about alpha (current)" in calls[0]
+
+
+@pytest.mark.unit
+def test_multi_chunk_with_multiple_questions_only_last_is_marked_current() -> None:
+    model_fn, calls = _spy_model()
+    chunks = [
+        {"source": "s1", "content": "alpha"},
+        {"source": "s2", "content": "beta"},
+    ]
+    questions = ["First question", "Second question", "Third question"]
+    Synthesizer(model_fn).synthesize(chunks, questions=questions)
+    prompt = calls[0]
+    assert "- Third question (current)" in prompt
+    assert "- First question\n" in prompt
+    assert "- Second question\n" in prompt
+    assert "First question (current)" not in prompt
+    assert "Second question (current)" not in prompt
+
+
+@pytest.mark.unit
+def test_multi_chunk_without_questions_prompt_contains_chunk_content_and_sources() -> None:
+    model_fn, calls = _spy_model()
+    chunks = [
+        {"source": "src_A", "content": "content alpha"},
+        {"source": "src_B", "content": "content beta"},
+    ]
+    Synthesizer(model_fn).synthesize(chunks)
+    assert len(calls) == 1
+    prompt = calls[0]
+    assert "content alpha" in prompt
+    assert "content beta" in prompt
+    assert "[Source: src_A]" in prompt
+    assert "[Source: src_B]" in prompt