feat: throw error on duplicate migration id (#46)

src/up.ts

@@ -10,6 +10,10 @@ export default async ({
   migrations: Migration[];
   migrationStore: MigrationStore;
 }): Promise<void> => {
+  if (migrations.length !== new Set(migrations.map((migration) => migration.id)).size) {
+    throw new Error('duplicate migration id');
+  }
+
   const appliedMigrations = await migrationStore.getAppliedMigrations();
   const migrationsToApply = migrations.filter(
     (migration) =>

test/up.test.ts

@@ -82,4 +82,21 @@ describe('up', () => {
     expect(migration1.up).toHaveBeenCalledTimes(1);
     expect(migration1.up).toHaveBeenCalledWith(context);
   });
+
+  it('should throw an error when duplicate migration IDs are passed', async () => {
+    expect.assertions(1);
+
+    // given
+    const migrations = [migration1, migration1];
+    MongoMigrationStoreMock.mockImplementationOnce(() => ({
+      init: vi.fn(),
+      getAppliedMigrations: vi.fn().mockReturnValueOnce([]),
+      insertMigration: vi.fn(),
+    }));
+    const migrationStore = new MongoMigrationStore();
+
+    // when
+    // then
+    await expect(() => up({ migrations, migrationStore })).rejects.toThrowError('duplicate migration id');
+  });
 });