Add initial SQLmem package structure with SQL parser, cache manager, column registry, and tests

tests/test_registry.py

@@ -0,0 +1,45 @@
+import sqlite3
+
+import pytest
+
+from sqlmem.registry import ColumnRegistry
+
+
+@pytest.fixture
+def registry():
+    conn = sqlite3.connect(":memory:")
+    return ColumnRegistry(conn)
+
+
+def test_empty_registry(registry):
+    assert registry.get_columns("users") == set()
+
+
+def test_update_and_get(registry):
+    registry.update("users", ["name", "email"])
+    assert registry.get_columns("users") == {"name", "email"}
+
+
+def test_update_accumulates(registry):
+    registry.update("users", ["name", "email"])
+    registry.update("users", ["email", "status"])
+    assert registry.get_columns("users") == {"name", "email", "status"}
+
+
+def test_needs_refetch_missing(registry):
+    registry.update("users", ["name"])
+    missing = registry.needs_refetch("users", ["name", "email"])
+    assert missing == ["email"]
+
+
+def test_needs_refetch_none_missing(registry):
+    registry.update("users", ["name", "email"])
+    missing = registry.needs_refetch("users", ["name"])
+    assert missing == []
+
+
+def test_independent_tables(registry):
+    registry.update("users", ["name"])
+    registry.update("orders", ["total"])
+    assert registry.get_columns("users") == {"name"}
+    assert registry.get_columns("orders") == {"total"}