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docs/docs/contributing/how_to/integrations/retriever_guide.md

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+---
+pagination_prev: contributing/how_to/integrations/index
+pagination_next: contributing/how_to/integrations/publish
+---
+# How to implement and test a retriever integration
+
+In this guide, we'll implement and test a custom [retriever](/docs/concepts/retrievers) that you have integrated with LangChain.
+
+For testing, we will rely on the `langchain-tests` dependency we added in the previous [package creation guide](/docs/contributing/how_to/integrations/package).
+
+## Implementation
+
+Let's say you're building a simple integration package that provides a `ToyRetriever`
+retriever integration for LangChain. Here's a simple example of what your project
+structure might look like:
+
+```plaintext
+langchain-parrot-link/
+├── langchain_parrot_link/
+│   ├── __init__.py
+│   └── retrievers.py
+├── tests/
+│   └── integration_tests
+|       ├── __init__.py
+|       └── test_retrievers.py
+├── pyproject.toml
+└── README.md
+```
+
+In this first step, we will implement the `retrievers.py` file
+
+import CustomRetrieverIntro from '/docs/how_to/_custom_retriever_intro.mdx';
+
+<CustomRetrieverIntro />
+
+<details>
+    <summary>retrievers.py</summary>
+```python title="langchain_parrot_link/retrievers.py"
+from typing import Any
+
+from langchain_core.callbacks import CallbackManagerForRetrieverRun
+from langchain_core.documents import Document
+from langchain_core.retrievers import BaseRetriever
+
+class ParrotRetriever(BaseRetriever):
+    parrot_name: str
+    k: int = 3
+
+    def _get_relevant_documents(
+        self, query: str, *, run_manager: CallbackManagerForRetrieverRun, **kwargs: Any
+    ) -> list[Document]:
+        k = kwargs.get("k", self.k)
+        return [Document(page_content=f"{self.parrot_name} says: {query}")] * k
+```
+</details>
+
+:::tip
+
+The `ParrotRetriever` from this guide is tested
+against the standard unit and integration tests in the LangChain Github repository.
+You can always use this as a starting point [here](https://github.com/langchain-ai/langchain/blob/master/libs/standard-tests/tests/unit_tests/test_basic_retriever.py).
+
+:::
+
+## Testing
+
+
+
+### 1. Create Your Retriever Class
+
+```python
+from langchain.schema import BaseRetriever, Document
+from langchain.callbacks.manager import CallbackManagerForRetrieverRun
+
+class MyCustomRetriever(BaseRetriever):
+    """Custom retriever implementation."""
+    
+    def _get_relevant_documents(
+        self, query: str, *, run_manager: CallbackManagerForRetrieverRun
+    ) -> List[Document]:
+        """Core implementation of retrieving relevant documents."""
+        # Your implementation here
+        pass
+
+    async def _aget_relevant_documents(
+        self, query: str, *, run_manager: CallbackManagerForRetrieverRun
+    ) -> List[Document]:
+        """Async implementation of retrieving relevant documents."""
+        # Your async implementation here
+        pass
+```
+
+### 2. Required Testing
+
+All retrievers must include the following tests:
+
+#### Basic Functionality Tests
+```python
+def test_get_relevant_documents():
+    retriever = MyCustomRetriever()
+    docs = retriever.get_relevant_documents("test query")
+    assert isinstance(docs, list)
+    assert all(isinstance(doc, Document) for doc in docs)
+
+@pytest.mark.asyncio
+async def test_aget_relevant_documents():
+    retriever = MyCustomRetriever()
+    docs = await retriever.aget_relevant_documents("test query")
+    assert isinstance(docs, list)
+    assert all(isinstance(doc, Document) for doc in docs)
+```
+
+#### Edge Cases
+- Empty query handling
+- Special character handling
+- Long query handling
+- Rate limiting (if applicable)
+- Error handling
+
+### 3. Documentation Requirements
+
+Your retriever should include:
+
+1. Class docstring with:
+   - General description
+   - Required dependencies
+   - Example usage
+   - Parameters explanation
+
+2. Integration documentation file:
+   - Installation instructions
+   - Basic usage example
+   - Advanced configuration
+   - Common issues and solutions
+
+### 4. Best Practices
+
+1. **Error Handling**
+   - Implement proper error handling for API calls
+   - Provide meaningful error messages
+   - Handle rate limits gracefully
+
+2. **Performance**
+   - Implement caching when appropriate
+   - Use batch operations where possible
+   - Consider implementing both sync and async methods
+
+3. **Configuration**
+   - Use environment variables for sensitive data
+   - Provide sensible defaults
+   - Allow for customization of key parameters
+
+4. **Type Hints**
+   - Use proper type hints throughout your code
+   - Document expected types in docstrings
+
+## Example Implementation
+
+Here's a minimal example of a custom retriever:
+
+```python
+from typing import List
+from langchain.schema import BaseRetriever, Document
+from langchain.callbacks.manager import CallbackManagerForRetrieverRun
+
+class SimpleKeywordRetriever(BaseRetriever):
+    """A simple retriever that matches documents based on keywords."""
+    
+    documents: List[Document]  # Store your documents here
+    
+    def _get_relevant_documents(
+        self, query: str, *, run_manager: CallbackManagerForRetrieverRun
+    ) -> List[Document]:
+        """Return documents that contain the query string."""
+        return [
+            doc for doc in self.documents 
+            if query.lower() in doc.page_content.lower()
+        ]
+
+    async def _aget_relevant_documents(
+        self, query: str, *, run_manager: CallbackManagerForRetrieverRun
+    ) -> List[Document]:
+        """Async version of get_relevant_documents."""
+        return self._get_relevant_documents(query, run_manager=run_manager)
+```
+
+## Submission Checklist
+
+- [ ] Implemented base retriever interface
+- [ ] Added comprehensive tests
+- [ ] Included proper documentation
+- [ ] Added type hints
+- [ ] Handled error cases
+- [ ] Implemented both sync and async methods
+- [ ] Added example usage
+- [ ] Followed code style guidelines
+- [ ] Added requirements.txt or setup.py updates
+
+## Getting Help
+
+If you need help while implementing your retriever:
+1. Check existing retriever implementations for reference
+2. Open a discussion in the GitHub repository
+3. Ask in the LangChain Discord community
+
+Remember to follow the existing patterns in the codebase and maintain consistency with other retrievers.

docs/docs/contributing/how_to/integrations/retriever_tests.md

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+# Standard Tests for LangChain Retrievers
+
+This guide outlines the standard tests that should be implemented for all LangChain retrievers.
+
+## Test Structure
+
+### 1. Basic Functionality Tests
+
+```python
+import pytest
+from langchain.schema import Document
+from your_retriever import YourRetriever
+
+def test_basic_retrieval():
+    """Test basic document retrieval functionality."""
+    retriever = YourRetriever()
+    query = "test query"
+    docs = retriever.get_relevant_documents(query)
+    
+    assert isinstance(docs, list)
+    assert all(isinstance(doc, Document) for doc in docs)
+    assert len(docs) > 0  # Adjust if your retriever might return empty results
+
+@pytest.mark.asyncio
+async def test_async_retrieval():
+    """Test async document retrieval functionality."""
+    retriever = YourRetriever()
+    query = "test query"
+    docs = await retriever.aget_relevant_documents(query)
+    
+    assert isinstance(docs, list)
+    assert all(isinstance(doc, Document) for doc in docs)
+```
+
+### 2. Edge Cases
+
+```python
+def test_empty_query():
+    """Test behavior with empty query."""
+    retriever = YourRetriever()
+    docs = retriever.get_relevant_documents("")
+    assert isinstance(docs, list)
+
+def test_special_characters():
+    """Test handling of special characters."""
+    retriever = YourRetriever()
+    special_queries = [
+        "test!@#$%^&*()",
+        "múltiple áccents",
+        "中文测试",
+        "test\nwith\nnewlines",
+    ]
+    for query in special_queries:
+        docs = retriever.get_relevant_documents(query)
+        assert isinstance(docs, list)
+
+def test_long_query():
+    """Test handling of very long queries."""
+    retriever = YourRetriever()
+    long_query = "test " * 1000
+    docs = retriever.get_relevant_documents(long_query)
+    assert isinstance(docs, list)
+```
+
+### 3. Error Handling
+
+```python
+def test_invalid_configuration():
+    """Test behavior with invalid configuration."""
+    with pytest.raises(ValueError):
+        YourRetriever(invalid_param="invalid")
+
+def test_connection_error():
+    """Test behavior when connection fails (if applicable)."""
+    retriever = YourRetriever()
+    # Mock connection failure
+    with pytest.raises(ConnectionError):
+        retriever.get_relevant_documents("test")
+```
+
+### 4. Performance Tests (Optional)
+
+```python
+@pytest.mark.slow
+def test_large_scale_retrieval():
+    """Test retrieval with a large number of documents."""
+    retriever = YourRetriever()
+    # Test with a significant number of documents
+    docs = retriever.get_relevant_documents("test")
+    assert len(docs) <= YOUR_MAX_LIMIT  # If applicable
+
+@pytest.mark.slow
+def test_concurrent_requests():
+    """Test handling of concurrent requests."""
+    import asyncio
+    
+    async def run_concurrent_requests():
+        retriever = YourRetriever()
+        tasks = [
+            retriever.aget_relevant_documents("test")
+            for _ in range(5)
+        ]
+        results = await asyncio.gather(*tasks)
+        return results
+    
+    results = asyncio.run(run_concurrent_requests())
+    assert len(results) == 5
+```
+
+### 5. Integration Tests
+
+```python
+def test_chain_integration():
+    """Test integration with LangChain chains."""
+    from langchain.chains import RetrievalQA
+    from langchain.llms import FakeLLM
+    
+    retriever = YourRetriever()
+    llm = FakeLLM()
+    qa_chain = RetrievalQA.from_chain_type(
+        llm=llm,
+        retriever=retriever,
+        chain_type="stuff"
+    )
+    result = qa_chain.run("test query")
+    assert isinstance(result, str)
+```
+
+## Test Configuration
+
+```python
+# conftest.py
+import pytest
+
+def pytest_configure(config):
+    config.addinivalue_line(
+        "markers", "slow: marks tests as slow (deselect with '-m \"not slow\"')"
+    )
+
+@pytest.fixture
+def sample_documents():
+    """Fixture providing sample documents for testing."""
+    return [
+        Document(page_content="test document 1", metadata={"source": "test1"}),
+        Document(page_content="test document 2", metadata={"source": "test2"}),
+    ]
+
+@pytest.fixture
+def mock_retriever(sample_documents):
+    """Fixture providing a retriever with sample documents."""
+    retriever = YourRetriever()
+    # Set up retriever with sample documents
+    return retriever
+```
+
+## Running Tests
+
+To run the tests:
+
+```bash
+# Run all tests
+pytest tests/retrievers/test_your_retriever.py
+
+# Run only fast tests
+pytest tests/retrievers/test_your_retriever.py -m "not slow"
+
+# Run with coverage
+pytest tests/retrievers/test_your_retriever.py --cov=your_retriever
+```
+
+## Best Practices
+
+1. **Isolation**: Each test should be independent and not rely on the state from other tests.
+
+2. **Mocking**: Use mocks for external services to avoid actual API calls during testing:
+   ```python
+   @pytest.fixture
+   def mock_api(mocker):
+       return mocker.patch("your_retriever.api_client")
+   ```
+
+3. **Parametrization**: Use pytest.mark.parametrize for testing multiple scenarios:
+   ```python
+   @pytest.mark.parametrize("query,expected_count", [
+       ("test", 1),
+       ("invalid", 0),
+       ("multiple words", 2),
+   ])
+   def test_retrieval_counts(query, expected_count):
+       retriever = YourRetriever()
+       docs = retriever.get_relevant_documents(query)
+       assert len(docs) == expected_count
+   ```
+
+4. **Documentation**: Include docstrings in test functions explaining what they test.
+
+5. **Coverage**: Aim for high test coverage, especially for core functionality.
+
+## Common Pitfalls
+
+1. Not testing error cases
+2. Not testing async functionality
+3. Not handling rate limits in tests
+4. Missing edge cases
+5. Relying on external services in unit tests
+
+Remember to adapt these tests based on your retriever's specific functionality and requirements.

docs/docs/how_to/_custom_retriever_intro.mdx

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+To create your own retriever, you need to extend the `BaseRetriever` class and implement the following methods:
+
+| Method                         | Description                                      | Required/Optional |
+|--------------------------------|--------------------------------------------------|-------------------|
+| `_get_relevant_documents`      | Get documents relevant to a query.               | Required          |
+| `_aget_relevant_documents`     | Implement to provide async native support.       | Optional          |
+
+
+The logic inside of `_get_relevant_documents` can involve arbitrary calls to a database or to the web using requests.
+
+:::tip
+By inherting from `BaseRetriever`, your retriever automatically becomes a LangChain [Runnable](/docs/concepts/runnables) and will gain the standard `Runnable` functionality out of the box!
+:::
+
+
+:::info
+You can use a `RunnableLambda` or `RunnableGenerator` to implement a retriever.
+
+The main benefit of implementing a retriever as a `BaseRetriever` vs. a `RunnableLambda` (a custom [runnable function](/docs/how_to/functions)) is that a `BaseRetriever` is a well
+known LangChain entity so some tooling for monitoring may implement specialized behavior for retrievers. Another difference
+is that a `BaseRetriever` will behave slightly differently from `RunnableLambda` in some APIs; e.g., the `start` event
+in `astream_events` API will be `on_retriever_start` instead of `on_chain_start`.
+:::

docs/docs/how_to/custom_retriever.ipynb

@@ -27,29 +27,9 @@
     "\n",
     "## Interface\n",
     "\n",
-    "To create your own retriever, you need to extend the `BaseRetriever` class and implement the following methods:\n",
+    "import CustomRetrieverIntro from './_custom_retriever_intro.mdx';\n",
     "\n",
-    "| Method                         | Description                                      | Required/Optional |\n",
-    "|--------------------------------|--------------------------------------------------|-------------------|\n",
-    "| `_get_relevant_documents`      | Get documents relevant to a query.               | Required          |\n",
-    "| `_aget_relevant_documents`     | Implement to provide async native support.       | Optional          |\n",
-    "\n",
-    "\n",
-    "The logic inside of `_get_relevant_documents` can involve arbitrary calls to a database or to the web using requests.\n",
-    "\n",
-    ":::tip\n",
-    "By inherting from `BaseRetriever`, your retriever automatically becomes a LangChain [Runnable](/docs/concepts/runnables) and will gain the standard `Runnable` functionality out of the box!\n",
-    ":::\n",
-    "\n",
-    "\n",
-    ":::info\n",
-    "You can use a `RunnableLambda` or `RunnableGenerator` to implement a retriever.\n",
-    "\n",
-    "The main benefit of implementing a retriever as a `BaseRetriever` vs. a `RunnableLambda` (a custom [runnable function](/docs/how_to/functions)) is that a `BaseRetriever` is a well\n",
-    "known LangChain entity so some tooling for monitoring may implement specialized behavior for retrievers. Another difference\n",
-    "is that a `BaseRetriever` will behave slightly differently from `RunnableLambda` in some APIs; e.g., the `start` event\n",
-    "in `astream_events` API will be `on_retriever_start` instead of `on_chain_start`.\n",
-    ":::\n"
+    "<CustomRetrieverIntro />"
    ]
   },
   {