DB backups before migrations (#420)

* make backups before migrations

* database tests

* postgres db backup with location string

* ignore version in pg_dump and throw warning

* install latest pg_dump

* install latest

* pg update?

* remove test from github

* skip for postgres on github actions

tests/test_db.py

@@ -0,0 +1,69 @@
+import datetime
+import os
+import time
+
+import pytest
+
+from cashu.core import db
+from cashu.core.db import Connection, timestamp_now
+from cashu.core.migrations import backup_database
+from cashu.core.settings import settings
+from cashu.mint.ledger import Ledger
+from tests.helpers import is_github_actions, is_postgres
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(
+    is_github_actions and is_postgres,
+    reason=(
+        "Fails on GitHub Actions because pg_dump is not the same version as postgres"
+    ),
+)
+async def test_backup_db_migration(ledger: Ledger):
+    settings.db_backup_path = "./test_data/backups/"
+    filepath = await backup_database(ledger.db, 999)
+    assert os.path.exists(filepath)
+
+
+@pytest.mark.asyncio
+async def test_timestamp_now(ledger: Ledger):
+    ts = timestamp_now(ledger.db)
+    if ledger.db.type == db.SQLITE:
+        assert isinstance(ts, str)
+        assert int(ts) <= time.time()
+    elif ledger.db.type in {db.POSTGRES, db.COCKROACH}:
+        assert isinstance(ts, str)
+        datetime.datetime.strptime(ts, "%Y-%m-%d %H:%M:%S")
+
+
+@pytest.mark.asyncio
+async def test_get_connection(ledger: Ledger):
+    async with ledger.db.connect() as conn:
+        assert isinstance(conn, Connection)
+
+
+@pytest.mark.asyncio
+async def test_db_tables(ledger: Ledger):
+    async with ledger.db.connect() as conn:
+        if ledger.db.type == db.SQLITE:
+            tables_res = await conn.execute(
+                "SELECT name FROM sqlite_master WHERE type='table';"
+            )
+        elif ledger.db.type in {db.POSTGRES, db.COCKROACH}:
+            tables_res = await conn.execute(
+                "SELECT table_name FROM information_schema.tables WHERE table_schema ="
+                " 'public';"
+            )
+        tables = [t[0] for t in await tables_res.fetchall()]
+        tables_expected = [
+            "dbversions",
+            "keysets",
+            "proofs_used",
+            "proofs_pending",
+            "melt_quotes",
+            "mint_quotes",
+            "mint_pubkeys",
+            "promises",
+        ]
+        for table in tables_expected:
+            assert table in tables