Add integration test to save and restore databases

extras/integration_tests/vm/test/save_and_restore_test.dart

@@ -0,0 +1,50 @@
+import 'dart:io';
+
+import 'package:moor_ffi/moor_ffi.dart';
+import 'package:path/path.dart';
+import 'package:test/test.dart';
+import 'package:tests/database/database.dart';
+
+final File mainFile =
+    File(join(Directory.systemTemp.path, 'moor-save-and-restore-tests-1'));
+final File createdForSwap =
+    File(join(Directory.systemTemp.path, 'moor-save-and-restore-tests-2'));
+
+void main() {
+  test('can save and restore a database', () async {
+    if (await mainFile.exists()) {
+      await mainFile.delete();
+    }
+    if (await createdForSwap.exists()) {
+      await createdForSwap.delete();
+    }
+
+    const nameInSwap = 'swap user';
+    const nameInMain = 'main';
+
+    // Prepare the file we're swapping in later
+    final dbForSetup = Database(VmDatabase(createdForSwap));
+    await dbForSetup.into(dbForSetup.users).insert(
+        UsersCompanion.insert(name: nameInSwap, birthDate: DateTime.now()));
+    await dbForSetup.close();
+
+    // Open the main file
+    var db = Database(VmDatabase(mainFile));
+    await db.into(db.users).insert(
+        UsersCompanion.insert(name: nameInMain, birthDate: DateTime.now()));
+    await db.close();
+
+    // Copy swap file to main file
+    await mainFile.writeAsBytes(await createdForSwap.readAsBytes(),
+        flush: true);
+
+    // Re-open database
+    db = Database(VmDatabase(mainFile));
+    final users = await db.select(db.users).get();
+
+    expect(
+      users.map((u) => u.name),
+      allOf(contains(nameInSwap), isNot(contains(nameInMain))),
+    );
+  });
+}