chore: migrations test (#3590)

## About the changes
This is a raw but working test for up and down migrations. 

In the first commit (before Andreas' fix:
https://github.com/Unleash/unleash/pull/3589) [it catches the migration
errors we
found](https://github.com/Unleash/unleash/actions/runs/4766567308/jobs/8473744864?pr=3590#step:5:605).
After merging from main the test go green, proving that it can catch
these issues earlier

src/test/e2e/helpers/database-init.ts

@@ -99,8 +99,7 @@ export default async function init(
 
     await db.raw(`DROP SCHEMA IF EXISTS ${config.db.schema} CASCADE`);
     await db.raw(`CREATE SCHEMA IF NOT EXISTS ${config.db.schema}`);
-    // @ts-expect-error
+    await migrateDb(config);
-    await migrateDb({ ...config, databaseSchema: config.db.schema });
     await db.destroy();
     const testDb = createDb(config);
     const stores = await createStores(config, testDb);

src/test/e2e/migrator.e2e.test.ts

@@ -0,0 +1,40 @@
+import { getDbConfig } from './helpers/database-config';
+import { createTestConfig } from '../config/test-config';
+import { getInstance } from 'db-migrate';
+import { Client } from 'pg';
+import { IDBOption } from 'lib/types';
+
+async function initSchema(db: IDBOption): Promise<void> {
+    const client = new Client(db);
+    await client.connect();
+    await client.query(`DROP SCHEMA IF EXISTS ${db.schema} CASCADE`);
+    await client.query(`CREATE SCHEMA IF NOT EXISTS ${db.schema}`);
+    await client.end();
+}
+
+test('Up & down migrations work', async () => {
+    const config = createTestConfig({
+        db: {
+            ...getDbConfig(),
+            pool: { min: 1, max: 4 },
+            schema: 'up_n_down_migrations_test',
+            ssl: false,
+        },
+    });
+
+    await initSchema(config.db);
+
+    const e2e = {
+        ...config.db,
+        connectionTimeoutMillis: 2000,
+    };
+
+    const dbm = getInstance(true, {
+        cwd: `${__dirname}/../../`, // relative to src/test/e2e
+        config: { e2e },
+        env: 'e2e',
+    });
+
+    await dbm.up();
+    await dbm.reset();
+});