refactor: Improve StringKnowledgeSource implementation

- Add logging functionality
- Add type hints and improve docstrings
- Organize tests into class structure
- Add edge case tests

Co-Authored-By: Joe Moura <joao@crewai.com>

src/crewai/knowledge/source/string_knowledge_source.py

@@ -3,31 +3,73 @@ from typing import List, Optional
 from pydantic import Field
 
 from crewai.knowledge.source.base_knowledge_source import BaseKnowledgeSource
+from crewai.knowledge.storage.knowledge_storage import KnowledgeStorage
+from crewai.utilities.logger import Logger
 
 
 class StringKnowledgeSource(BaseKnowledgeSource):
     """A knowledge source that stores and queries plain text content using embeddings."""
 
+    _logger: Logger = Logger(verbose=True)
     content: str = Field(...)
     collection_name: Optional[str] = Field(default=None)
 
-    def model_post_init(self, _):
-        """Post-initialization method to validate content."""
-        self.validate_content()
+    def model_post_init(self, _) -> None:
+        """Post-initialization method to validate content and initialize storage.
+        
+        This method is called after the model is initialized to perform content validation
+        and set up the knowledge storage system. It ensures that:
+        1. The content is a valid string
+        2. The storage system is properly initialized
+        
+        Raises:
+            ValueError: If content validation fails or storage initialization fails
+        """
+        try:
+            self.validate_content()
+            if self.storage is None:
+                self.storage = KnowledgeStorage(collection_name=self.collection_name)
+            self.storage.initialize_knowledge_storage()
+        except Exception as e:
+            error_msg = f"Failed to initialize knowledge storage: {str(e)}"
+            self._logger.log("error", error_msg, "red")
+            raise ValueError(error_msg)
 
-    def validate_content(self):
-        """Validate string content."""
-        if not isinstance(self.content, str):
-            raise ValueError("StringKnowledgeSource only accepts string content")
+    def validate_content(self) -> None:
+        """Validate that the content is a valid string.
+        
+        Raises:
+            ValueError: If content is not a string or is empty
+        """
+        if not isinstance(self.content, str) or not self.content.strip():
+            error_msg = "StringKnowledgeSource only accepts string content"
+            self._logger.log("error", error_msg, "red")
+            raise ValueError(error_msg)
 
     def add(self) -> None:
-        """Add string content to the knowledge source, chunk it, compute embeddings, and save them."""
+        """Add string content to the knowledge source, chunk it, compute embeddings, and save them.
+        
+        This method processes the content by:
+        1. Chunking the text into smaller pieces
+        2. Adding the chunks to the source
+        3. Computing embeddings and saving them
+        
+        Raises:
+            ValueError: If storage is not initialized when trying to save documents
+        """
         new_chunks = self._chunk_text(self.content)
         self.chunks.extend(new_chunks)
         self._save_documents()
 
     def _chunk_text(self, text: str) -> List[str]:
-        """Utility method to split text into chunks."""
+        """Split text into chunks based on chunk_size and chunk_overlap.
+        
+        Args:
+            text: The text to split into chunks
+            
+        Returns:
+            List[str]: List of text chunks
+        """
         return [
             text[i : i + self.chunk_size]
             for i in range(0, len(text), self.chunk_size - self.chunk_overlap)

tests/knowledge/knowledge_test.py

@@ -5,6 +5,7 @@ from typing import List, Union
 from unittest.mock import patch
 
 import pytest
+from pydantic import ValidationError
 
 from crewai.knowledge.source.crew_docling_source import CrewDoclingSource
 from crewai.knowledge.source.csv_knowledge_source import CSVKnowledgeSource
@@ -37,6 +38,42 @@ def reset_knowledge_storage(mock_vector_db):
     yield
 
 
+class TestStringKnowledgeSource:
+    def test_initialization(self, mock_vector_db):
+        """Test basic initialization of StringKnowledgeSource."""
+        content = "Users name is John. He is 30 years old and lives in San Francisco."
+        string_source = StringKnowledgeSource(content=content)
+        assert string_source.content == content
+        assert string_source.storage is not None
+
+    def test_add_and_query(self, mock_vector_db):
+        """Test adding content and querying."""
+        content = "Users name is John. He is 30 years old and lives in San Francisco."
+        string_source = StringKnowledgeSource(content=content)
+        string_source.storage = mock_vector_db
+
+        mock_vector_db.query.return_value = [{"context": content, "score": 0.9}]
+
+        string_source.add()
+        assert len(string_source.chunks) > 0
+
+        query = "Where does John live?"
+        results = mock_vector_db.query(query)
+        assert len(results) > 0
+        assert "San Francisco" in results[0]["context"]
+        mock_vector_db.query.assert_called_once()
+
+    def test_empty_content(self, mock_vector_db):
+        """Test that empty content raises ValueError."""
+        with pytest.raises(ValueError, match="StringKnowledgeSource only accepts string content"):
+            StringKnowledgeSource(content="")
+
+    def test_non_string_content(self, mock_vector_db):
+        """Test that non-string content raises ValidationError."""
+        with pytest.raises(ValidationError, match="Input should be a valid string"):
+            StringKnowledgeSource(content=123)
+
+
 def test_single_short_string(mock_vector_db):
     # Create a knowledge base with a single short string
     content = "Brandon's favorite color is blue and he likes Mexican food."
@@ -418,6 +455,9 @@ def test_hybrid_string_and_files(mock_vector_db, tmpdir):
     mock_vector_db.query.assert_called_once()
 
 
+
+
+
 def test_pdf_knowledge_source(mock_vector_db):
     # Get the directory of the current file
     current_dir = Path(__file__).parent