test(backend): Add pytest testing infrastructure

- Add pytest, pytest-asyncio, pytest-mock to dev dependencies
- Configure pytest in pyproject.toml with async support
- Create tests directory structure with conftest.py
- Set up unit test framework for connector testing
- Enable automated testing for backend components

surfsense_backend/tests/conftest.py

@@ -0,0 +1,104 @@
+"""Shared pytest fixtures for SurfSense backend tests."""
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
+from sqlalchemy.orm import sessionmaker
+
+from app.db import Base
+
+
+@pytest.fixture
+async def async_session():
+    """Create an async database session for testing."""
+    from sqlalchemy import JSON, ARRAY, event
+    from sqlalchemy.dialects.postgresql import JSONB
+    
+    # Use in-memory SQLite for tests
+    engine = create_async_engine(
+        "sqlite+aiosqlite:///:memory:",
+        echo=False,
+    )
+
+    # Replace JSONB and ARRAY with JSON for SQLite compatibility
+    @event.listens_for(Base.metadata, "before_create")
+    def _set_json_type(target, connection, **kw):
+        for table in Base.metadata.tables.values():
+            for column in table.columns:
+                # Convert JSONB to JSON
+                if isinstance(column.type, type(JSONB())):
+                    column.type = JSON()
+                # Convert ARRAY to JSON (SQLite doesn't support ARRAY)
+                elif isinstance(column.type, ARRAY):
+                    column.type = JSON()
+
+    # Create tables
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+    # Create session
+    async_session_maker = sessionmaker(
+        engine, class_=AsyncSession, expire_on_commit=False
+    )
+
+    async with async_session_maker() as session:
+        yield session
+
+    # Cleanup
+    await engine.dispose()
+
+
+@pytest.fixture
+def mock_connector_config():
+    """Mock connector configuration."""
+    return {
+        "tokens": [
+            {
+                "chain": "ethereum",
+                "address": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
+                "name": "WETH",
+            },
+            {
+                "chain": "solana",
+                "address": "So11111111111111111111111111111111111111112",
+                "name": "SOL",
+            },
+        ]
+    }
+
+
+@pytest.fixture
+def mock_pair_data():
+    """Mock DexScreener API response data."""
+    return {
+        "pairs": [
+            {
+                "chainId": "ethereum",
+                "dexId": "uniswap",
+                "url": "https://dexscreener.com/ethereum/0x123",
+                "pairAddress": "0x123",
+                "baseToken": {
+                    "address": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
+                    "name": "Wrapped Ether",
+                    "symbol": "WETH",
+                },
+                "quoteToken": {
+                    "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
+                    "name": "USD Coin",
+                    "symbol": "USDC",
+                },
+                "priceNative": "1.0",
+                "priceUsd": "2500.00",
+                "txns": {
+                    "m5": {"buys": 10, "sells": 5},
+                    "h1": {"buys": 100, "sells": 50},
+                    "h6": {"buys": 500, "sells": 250},
+                    "h24": {"buys": 2000, "sells": 1000},
+                },
+                "volume": {"h24": 1000000.0, "h6": 250000.0, "h1": 50000.0, "m5": 5000.0},
+                "priceChange": {"m5": 0.5, "h1": 1.2, "h6": 2.5, "h24": 5.0},
+                "liquidity": {"usd": 5000000.0, "base": 2000.0, "quote": 5000000.0},
+                "fdv": 10000000.0,
+                "pairCreatedAt": 1609459200000,
+            }
+        ]
+    }