diff --git a/src/memory/common/db/models/source_item.py b/src/memory/common/db/models/source_item.py
index 49c66b4..b7ed5ae 100644
--- a/src/memory/common/db/models/source_item.py
+++ b/src/memory/common/db/models/source_item.py
@@ -347,7 +347,7 @@ class SourceItem(Base):
             collection_name=modality,
             embedding_model=collections.collection_model(modality, text, images),
             item_metadata=extract.merge_metadata(
-                self.as_payload(), data.metadata, metadata
+                cast(dict[str, Any], self.as_payload()), data.metadata, metadata
             ),
         )
         return chunk
diff --git a/src/memory/common/db/models/users.py b/src/memory/common/db/models/users.py
index 5c81d77..1e0ea4f 100644
--- a/src/memory/common/db/models/users.py
+++ b/src/memory/common/db/models/users.py
@@ -15,7 +15,6 @@ from sqlalchemy import (
 )
 from sqlalchemy.sql import func
 from sqlalchemy.orm import relationship
-from datetime import datetime
 
 
 def hash_password(password: str) -> str:
diff --git a/tests/memory/common/db/models/test_source_item.py b/tests/memory/common/db/models/test_source_item.py
index 0b47372..b2bba9a 100644
--- a/tests/memory/common/db/models/test_source_item.py
+++ b/tests/memory/common/db/models/test_source_item.py
@@ -547,3 +547,141 @@ def test_subclass_deletion_cascades_from_source_item(db_session: Session):
     # Verify both the MailMessage and SourceItem records are deleted
     assert db_session.query(MailMessage).filter_by(id=mail_message_id).first() is None
     assert db_session.query(SourceItem).filter_by(id=source_item_id).first() is None
+
+
+@pytest.mark.parametrize(
+    "content,image_paths,expected_chunks",
+    [
+        ("", [], 0),  # Empty content returns empty list
+        ("   \n  ", [], 0),  # Whitespace-only content returns empty list
+        ("Short content", [], 1),  # Short content returns just full_text chunk
+        ("A" * 10, [], 1),  # Very short content returns just full_text chunk
+    ],
+)
+def test_chunk_mixed_basic_cases(tmp_path, content, image_paths, expected_chunks):
+    """Test chunk_mixed function with basic cases"""
+    from memory.common.db.models.source_item import chunk_mixed
+
+    # Create test images if needed
+    actual_image_paths = []
+    for i, _ in enumerate(image_paths):
+        image_file = tmp_path / f"test{i}.png"
+        img = Image.new("RGB", (1, 1), color="red")
+        img.save(image_file)
+        actual_image_paths.append(image_file.name)
+
+    # Mock settings.FILE_STORAGE_DIR to point to tmp_path
+    with patch.object(settings, "FILE_STORAGE_DIR", tmp_path):
+        result = chunk_mixed(content, actual_image_paths)
+
+    assert len(result) == expected_chunks
+
+
+def test_chunk_mixed_with_images(tmp_path):
+    """Test chunk_mixed function with images"""
+    from memory.common.db.models.source_item import chunk_mixed
+
+    # Create test images
+    image1 = tmp_path / "image1.png"
+    image2 = tmp_path / "image2.jpg"
+    Image.new("RGB", (1, 1), color="red").save(image1)
+    Image.new("RGB", (1, 1), color="blue").save(image2)
+
+    content = "This content mentions image1.png and image2.jpg"
+    image_paths = [image1.name, image2.name]
+
+    with patch.object(settings, "FILE_STORAGE_DIR", tmp_path):
+        result = chunk_mixed(content, image_paths)
+
+    assert len(result) >= 1
+    # First chunk should contain the full text and images
+    assert content.strip() in result[0].data
+    assert len([d for d in result[0].data if isinstance(d, Image.Image)]) == 2
+
+
+def test_chunk_mixed_long_content(tmp_path):
+    """Test chunk_mixed function with long content that gets chunked"""
+    from memory.common.db.models.source_item import chunk_mixed
+
+    # Create long content
+    long_content = "Lorem ipsum dolor sit amet, " * 50  # About 150 words
+
+    # Mock the chunker functions to force chunking behavior
+    with (
+        patch.object(settings, "FILE_STORAGE_DIR", tmp_path),
+        patch.object(chunker, "DEFAULT_CHUNK_TOKENS", 10),
+        patch.object(chunker, "approx_token_count", return_value=100),
+    ):  # Force it to be > 2 * 10
+        result = chunk_mixed(long_content, [])
+
+    # Should have multiple chunks: full_text + chunked pieces + summary
+    assert len(result) > 1
+
+    # First chunk should be full text
+    assert long_content.strip() in result[0].data
+
+    # Last chunk should be summary
+    # (we can't easily test the exact summary without mocking summarizer)
+    assert result[-1].data  # Should have some data
+
+
+@pytest.mark.parametrize(
+    "sha256_values,expected_committed",
+    [
+        ([b"unique1", b"unique2", b"unique3"], 3),  # All unique
+        ([b"duplicate", b"duplicate", b"unique"], 2),  # One duplicate pair
+        ([b"same", b"same", b"same"], 1),  # All duplicates
+        ([b"dup1", b"dup1", b"dup2", b"dup2"], 2),  # Two duplicate pairs
+    ],
+)
+def test_handle_duplicate_sha256_behavior(
+    db_session: Session, sha256_values, expected_committed
+):
+    """Test that handle_duplicate_sha256 event listener prevents duplicate sha256 values"""
+    # Create SourceItems with the given sha256 values
+    items = []
+    for i, sha256 in enumerate(sha256_values):
+        item = SourceItem(sha256=sha256, content=f"test content {i}", modality="text")
+        items.append(item)
+        db_session.add(item)
+
+    # Commit should trigger the event listener
+    db_session.commit()
+
+    # Query how many items were actually committed
+    committed_count = db_session.query(SourceItem).count()
+    assert committed_count == expected_committed
+
+    # Verify all sha256 values in database are unique
+    sha256_in_db = [row[0] for row in db_session.query(SourceItem.sha256).all()]
+    assert len(sha256_in_db) == len(set(sha256_in_db))  # All unique
+
+
+def test_handle_duplicate_sha256_with_existing_data(db_session: Session):
+    """Test duplicate handling when items already exist in database"""
+    # Add initial items
+    existing_item = SourceItem(sha256=b"existing", content="original", modality="text")
+    db_session.add(existing_item)
+    db_session.commit()
+
+    # Try to add new items with same and different sha256
+    new_items = [
+        SourceItem(
+            sha256=b"existing", content="duplicate", modality="text"
+        ),  # Should be rejected
+        SourceItem(
+            sha256=b"new_unique", content="new content", modality="text"
+        ),  # Should be kept
+    ]
+    for item in new_items:
+        db_session.add(item)
+
+    db_session.commit()
+
+    # Should have 2 items total (original + new unique)
+    assert db_session.query(SourceItem).count() == 2
+
+    # Original content should be preserved
+    existing_in_db = db_session.query(SourceItem).filter_by(sha256=b"existing").first()
+    assert existing_in_db is not None
+    assert str(existing_in_db.content) == "original"  # Original should be preserved
diff --git a/tests/memory/common/db/models/test_users.py b/tests/memory/common/db/models/test_users.py
new file mode 100644
index 0000000..56b0473
--- /dev/null
+++ b/tests/memory/common/db/models/test_users.py
@@ -0,0 +1,104 @@
+import pytest
+from memory.common.db.models.users import hash_password, verify_password
+
+
+@pytest.mark.parametrize(
+    "password",
+    [
+        "simple_password",
+        "complex_P@ssw0rd!",
+        "very_long_password_with_many_characters_1234567890",
+        "",
+        "unicode_password_тест_😀",
+        "password with spaces",
+    ],
+)
+def test_hash_password_format(password):
+    """Test that hash_password returns correctly formatted hash"""
+    result = hash_password(password)
+
+    # Should be in format "salt:hash"
+    assert ":" in result
+    parts = result.split(":", 1)
+    assert len(parts) == 2
+
+    salt, hash_value = parts
+    # Salt should be 32 hex characters (16 bytes * 2)
+    assert len(salt) == 32
+    assert all(c in "0123456789abcdef" for c in salt)
+
+    # Hash should be 64 hex characters (SHA-256 = 32 bytes * 2)
+    assert len(hash_value) == 64
+    assert all(c in "0123456789abcdef" for c in hash_value)
+
+
+def test_hash_password_uniqueness():
+    """Test that same password generates different hashes due to random salt"""
+    password = "test_password"
+    hash1 = hash_password(password)
+    hash2 = hash_password(password)
+
+    # Different salts should produce different hashes
+    assert hash1 != hash2
+
+    # But both should verify correctly
+    assert verify_password(password, hash1)
+    assert verify_password(password, hash2)
+
+
+@pytest.mark.parametrize(
+    "password,expected",
+    [
+        ("correct_password", True),
+        ("wrong_password", False),
+        ("", False),
+        ("CORRECT_PASSWORD", False),  # Case sensitive
+    ],
+)
+def test_verify_password_correctness(password, expected):
+    """Test password verification with correct and incorrect passwords"""
+    correct_password = "correct_password"
+    password_hash = hash_password(correct_password)
+
+    result = verify_password(password, password_hash)
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "malformed_hash",
+    [
+        "invalid_format",
+        "no_colon_here",
+        ":empty_salt",
+        "salt:",  # Empty hash
+        "",
+        "too:many:colons:here",
+        "salt:invalid_hex_zzz",
+        "salt:too_short_hash",
+    ],
+)
+def test_verify_password_malformed_hash(malformed_hash):
+    """Test that verify_password handles malformed hashes gracefully"""
+    result = verify_password("any_password", malformed_hash)
+    assert result is False
+
+
+@pytest.mark.parametrize(
+    "test_password",
+    [
+        "simple",
+        "complex_P@ssw0rd!123",
+        "",
+        "unicode_тест_😀",
+        "password with spaces and symbols !@#$%^&*()",
+    ],
+)
+def test_hash_verify_roundtrip(test_password):
+    """Test that hash and verify work correctly together"""
+    password_hash = hash_password(test_password)
+
+    # Correct password should verify
+    assert verify_password(test_password, password_hash)
+
+    # Wrong password should not verify
+    assert not verify_password(test_password + "_wrong", password_hash)
diff --git a/tests/memory/common/test_embedding.py b/tests/memory/common/test_embedding.py
index 91fd2f4..7e45a59 100644
--- a/tests/memory/common/test_embedding.py
+++ b/tests/memory/common/test_embedding.py
@@ -1,23 +1,30 @@
 from unittest.mock import Mock
 import pytest
+from typing import cast
+from PIL import Image
 
-from memory.common import collections
+from memory.common import collections, settings
 from memory.common.embedding import (
+    as_string,
+    embed_chunks,
     embed_mixed,
     embed_text,
+    break_chunk,
+    embed_by_model,
 )
-from memory.common.extract import DataChunk
+from memory.common.extract import DataChunk, MulitmodalChunk
+from memory.common.db.models import Chunk, SourceItem
 
 
 @pytest.fixture
 def mock_embed(mock_voyage_client):
     vectors = ([i] for i in range(1000))
 
-    def embed(texts, model, input_type):
+    def embed_func(texts, model, input_type):
         return Mock(embeddings=[next(vectors) for _ in texts])
 
-    mock_voyage_client.embed = embed
-    mock_voyage_client.multimodal_embed = embed
+    mock_voyage_client.embed = Mock(side_effect=embed_func)
+    mock_voyage_client.multimodal_embed = Mock(side_effect=embed_func)
 
     return mock_voyage_client
 
@@ -52,3 +59,182 @@ def test_embed_text(mock_embed):
 def test_embed_mixed(mock_embed):
     items = [DataChunk(data=["text"])]
     assert embed_mixed(items) == [[0]]
+
+
+@pytest.mark.parametrize(
+    "input_data, expected_output",
+    [
+        ("hello world", "hello world"),
+        ("  hello world  \n", "hello world"),
+        (
+            cast(list[MulitmodalChunk], ["first chunk", "second chunk", "third chunk"]),
+            "first chunk\nsecond chunk\nthird chunk",
+        ),
+        (cast(list[MulitmodalChunk], []), ""),
+        (
+            cast(list[MulitmodalChunk], ["", "valid text", "  ", "another text"]),
+            "valid text\n\nanother text",
+        ),
+    ],
+)
+def test_as_string_basic_cases(input_data, expected_output):
+    assert as_string(input_data) == expected_output
+
+
+def test_as_string_with_nested_lists():
+    # This tests the recursive nature of as_string - kept separate due to different input type
+    chunks = [["nested", "items"], "single item"]
+    result = as_string(chunks)
+    assert result == "nested\nitems\nsingle item"
+
+
+def test_embed_chunks_with_text_model(mock_embed):
+    chunks = cast(list[list[MulitmodalChunk]], [["text1"], ["text2"]])
+    result = embed_chunks(chunks, model=settings.TEXT_EMBEDDING_MODEL)
+    assert result == [[0], [1]]
+    mock_embed.embed.assert_called_once_with(
+        ["text1", "text2"],
+        model=settings.TEXT_EMBEDDING_MODEL,
+        input_type="document",
+    )
+
+
+def test_embed_chunks_with_mixed_model(mock_embed):
+    chunks = cast(list[list[MulitmodalChunk]], [["text with image"], ["another chunk"]])
+    result = embed_chunks(chunks, model=settings.MIXED_EMBEDDING_MODEL)
+    assert result == [[0], [1]]
+    mock_embed.multimodal_embed.assert_called_once_with(
+        chunks, model=settings.MIXED_EMBEDDING_MODEL, input_type="document"
+    )
+
+
+def test_embed_chunks_with_query_input_type(mock_embed):
+    chunks = cast(list[list[MulitmodalChunk]], [["query text"]])
+    result = embed_chunks(chunks, input_type="query")
+    assert result == [[0]]
+    mock_embed.embed.assert_called_once_with(
+        ["query text"], model=settings.TEXT_EMBEDDING_MODEL, input_type="query"
+    )
+
+
+def test_embed_chunks_empty_list(mock_embed):
+    result = embed_chunks([])
+    assert result == []
+
+
+@pytest.mark.parametrize(
+    "data, chunk_size, expected_result",
+    [
+        (["short text"], 100, ["short text"]),
+        (["some text content"], 200, ["some text content"]),
+        ([], 100, []),
+    ],
+)
+def test_break_chunk_simple_cases(data, chunk_size, expected_result):
+    chunk = DataChunk(data=data)
+    result = break_chunk(chunk, chunk_size=chunk_size)
+    assert result == expected_result
+
+
+def test_break_chunk_with_long_text():
+    # Create text that will exceed chunk size
+    long_text = "word " * 200  # Should be much longer than default chunk size
+    chunk = DataChunk(data=[long_text])
+    result = break_chunk(chunk, chunk_size=50)
+
+    # Should be broken into multiple chunks
+    assert len(result) > 1
+    assert all(isinstance(item, str) for item in result)
+
+
+def test_break_chunk_with_mixed_data_types():
+    # Mock image object
+    mock_image = Mock(spec=Image.Image)
+    chunk = DataChunk(data=["text content", mock_image])
+    result = break_chunk(chunk, chunk_size=100)
+
+    # Should have text chunks plus the original chunk (since it's not a string)
+    assert len(result) >= 2
+    assert any(isinstance(item, str) for item in result)
+    # The original chunk should be preserved when it contains mixed data
+    assert chunk in result
+
+
+def test_embed_by_model_with_matching_chunks(mock_embed):
+    # Create mock chunks with specific embedding model
+    chunk1 = Mock(spec=Chunk)
+    chunk1.embedding_model = "test-model"
+    chunk1.chunks = ["chunk1 content"]
+
+    chunk2 = Mock(spec=Chunk)
+    chunk2.embedding_model = "test-model"
+    chunk2.chunks = ["chunk2 content"]
+
+    chunks = cast(list[Chunk], [chunk1, chunk2])
+    result = embed_by_model(chunks, "test-model")
+
+    assert len(result) == 2
+    assert chunk1.vector == [0]
+    assert chunk2.vector == [1]
+    assert result == [chunk1, chunk2]
+
+
+def test_embed_by_model_with_no_matching_chunks(mock_embed):
+    chunk1 = Mock(spec=Chunk)
+    chunk1.embedding_model = "different-model"
+    # Ensure the chunk doesn't have a vector initially
+    del chunk1.vector
+
+    chunks = cast(list[Chunk], [chunk1])
+    result = embed_by_model(chunks, "test-model")
+
+    assert result == []
+    assert not hasattr(chunk1, "vector")
+
+
+def test_embed_by_model_with_mixed_models(mock_embed):
+    chunk1 = Mock(spec=Chunk)
+    chunk1.embedding_model = "test-model"
+    chunk1.chunks = ["chunk1 content"]
+
+    chunk2 = Mock(spec=Chunk)
+    chunk2.embedding_model = "other-model"
+    chunk2.chunks = ["chunk2 content"]
+
+    chunk3 = Mock(spec=Chunk)
+    chunk3.embedding_model = "test-model"
+    chunk3.chunks = ["chunk3 content"]
+
+    chunks = cast(list[Chunk], [chunk1, chunk2, chunk3])
+    result = embed_by_model(chunks, "test-model")
+
+    assert len(result) == 2
+    assert chunk1 in result
+    assert chunk3 in result
+    assert chunk2 not in result
+    assert chunk1.vector == [0]
+    assert chunk3.vector == [1]
+
+
+def test_embed_by_model_with_empty_chunks(mock_embed):
+    result = embed_by_model([], "test-model")
+    assert result == []
+
+
+def test_embed_by_model_calls_embed_chunks_correctly(mock_embed):
+    chunk1 = Mock(spec=Chunk)
+    chunk1.embedding_model = "test-model"
+    chunk1.chunks = ["content1"]
+
+    chunk2 = Mock(spec=Chunk)
+    chunk2.embedding_model = "test-model"
+    chunk2.chunks = ["content2"]
+
+    chunks = cast(list[Chunk], [chunk1, chunk2])
+    embed_by_model(chunks, "test-model")
+
+    # Verify embed_chunks was called with the right model
+    expected_chunks = [["content1"], ["content2"]]
+    mock_embed.embed.assert_called_once_with(
+        ["content1", "content2"], model="test-model", input_type="document"
+    )