Add test to unmigrate test models

butane/tests/unmigrate.rs

@@ -0,0 +1,42 @@
+//! Test the "current" migration created by the butane_test_helper due to
+//! all of the other tests in the butane/tests directory.
+#![cfg(test)]
+use butane::db::{BackendConnection, Connection};
+use butane::migrations::{self, MemMigrations, Migration, Migrations, MigrationsMut};
+use butane_test_helper::*;
+
+fn unmigrate(mut connection: Connection) {
+    let base_dir = std::path::PathBuf::from(".butane");
+    let root = base_dir.join("migrations");
+    let mut disk_migrations = migrations::from_root(root);
+
+    // this reproduces the migration created in butane_test_helper::setup_db
+    let disk_current = disk_migrations.current();
+    let mut mem_migrations = MemMigrations::new();
+    let mem_current = mem_migrations.current();
+    migrations::copy_migration(disk_current, mem_current).unwrap();
+
+    assert!(
+        disk_current.db().unwrap().tables().count() != 0,
+        "No tables to migrate"
+    );
+
+    let backend_name = connection.backend_name();
+    let backend = butane::db::get_backend(backend_name).unwrap();
+    assert!(
+        mem_migrations
+            .create_migration(&nonempty::nonempty![backend], "init", None)
+            .expect("expected to create migration without error"),
+        "expected to create migration"
+    );
+
+    let migrations = mem_migrations.unapplied_migrations(&connection).unwrap();
+    assert_eq!(migrations.len(), 0);
+
+    let migration = mem_migrations.latest().unwrap();
+    migration.downgrade(&mut connection).unwrap();
+
+    let migrations = mem_migrations.unapplied_migrations(&connection).unwrap();
+    assert_eq!(migrations.len(), 1);
+}
+testall!(unmigrate);