Support for :memory: databases

If you start Datasette with no files, it will connect to :memory: instead.

When starting it with files you can add --memory to also get a :memory: database.

tests/fixtures.py

@@ -65,6 +65,14 @@ def app_client():
     yield from make_app_client()
 
 
+@pytest.fixture(scope="session")
+def app_client_no_files():
+    ds = Datasette([])
+    client = TestClient(ds.app().test_client)
+    client.ds = ds
+    yield client
+
+
 @pytest.fixture(scope='session')
 def app_client_shorter_time_limit():
     yield from make_app_client(20)

tests/test_api.py

@@ -1,5 +1,6 @@
 from .fixtures import ( # noqa
     app_client,
+    app_client_no_files,
     app_client_shorter_time_limit,
     app_client_larger_cache_size,
     app_client_returned_rows_matches_page_size,
@@ -368,6 +369,31 @@ def test_database_page(app_client):
     }] == data['tables']
 
 
+def test_no_files_uses_memory_database(app_client_no_files):
+    response = app_client_no_files.get("/.json")
+    assert response.status == 200
+    assert {
+        ":memory:": {
+            "hash": "000",
+            "hidden_table_rows_sum": 0,
+            "hidden_tables_count": 0,
+            "name": ":memory:",
+            "path": ":memory:-000",
+            "table_rows_sum": 0,
+            "tables_count": 0,
+            "tables_more": False,
+            "tables_truncated": [],
+            "views_count": 0,
+        }
+    } == response.json
+    # Try that SQL query
+    response = app_client_no_files.get(
+        "/:memory:-0.json?sql=select+sqlite_version()&_shape=array"
+    )
+    assert 1 == len(response.json)
+    assert ["sqlite_version()"] == list(response.json[0].keys())
+
+
 def test_database_page_for_database_with_dot_in_name(app_client_with_dot):
     response = app_client_with_dot.get("/fixtures.dot.json")
     assert 200 == response.status