Create schema submodule holding versioned schemas

This is meant to hold schemas and migrations. It contains an
`__init__.py` due to a limitation of `importlib.resources` outlined in
detail here: https://github.com/python/importlib_resources/issues/58

Eventually the schema submodule will handle automatic migration of older
databases when importing into new stores.

src/nancy/db.py

@@ -8,16 +8,13 @@ import sqlite3
 schema_version = 0
 
 
-def init(path):
-    """
-    Initialize a data store directory.
-    """
-    if os.path.exists(path):
-        raise FileExistsError(f"Refusing to overwrite existing database {path}")
-    schema = importlib.resources.open_text("nancy", "schema.sql").read()
-    conn = sqlite3.connect(path)
-    conn.cursor().executescript(schema)
-    return conn
+def init_schema(cur):
+    """Initialize a database following the current schema."""
+    schema = importlib.resources.read_text(
+        "nancy.schema",
+        f"version{schema_version}.sql",
+    )
+    cur.executescript(schema)
 
 
 def connect(path):

src/nancy/store.py

@@ -59,9 +59,8 @@ class Store:
                     f"File {db_path} exists. Refusing to re-initialize",
                 )
         # initialize a database in the target directory
-        schema = importlib.resources.open_text("nancy", "schema.sql").read()
         conn = sqlite3.connect(db_path)
-        conn.cursor().executescript(schema)
+        db.init_schema(conn.cursor())
         new_store = cls(directory, conn)
 
         new_store.record_machine_description()

tests/test_db.py

@@ -10,17 +10,13 @@ import sqlite3
 @pytest.fixture
 def temp_db():
     """Create an in-memory database that follow's the nancy schema"""
-    conn = sqlite3.connect(':memory:')
+    with sqlite3.connect(':memory:') as conn:
         cur = conn.cursor()
-    #import importlib
-    #schema = importlib.resources.open_text("nancy", "schema.sql").read()
-    schema = open(os.path.join(
-            os.path.dirname(__file__),
-            '../src/nancy/schema.sql',
-        ), 'r').read()
-    cur.executescript(schema)
+
+        from nancy import db
+        db.init_schema(cur)
+
         yield cur
-    conn.close()
 
 
 @pytest.fixture