Skip to main content

Mocking ORMs

What this covers: Mocking Object-Relational Mapping (ORM) libraries like TypeORM, Prisma, Drizzle, and MikroORM
Time to read: ~12 minutes
Prerequisites: Unit Testing Fundamentals, Solitary Unit Tests
Best for: Testing services that interact with databases without hitting real database connections

When testing services that interact with databases, you need to mock ORM clients to keep tests isolated. This guide shows you how to structure your code and write tests for popular ORMs: TypeORM, Prisma, Drizzle, and MikroORM.

Overview​

This guide covers:

  1. The pattern: Wrapping ORM clients in injectables
  2. TypeORM: Mocking repositories and entity managers
  3. Prisma: Mocking Prisma client instances
  4. Drizzle: Mocking Drizzle database instances
  5. MikroORM: Mocking entity managers and repositories

The Pattern: Wrap ORM Clients with Injectables​

ORMs typically provide clients or managers that you import directly. To make them mockable with Suites, wrap them in injectable classes that your business logic depends on.

Why wrap ORM clients?

  • Explicit dependencies: Suites can only mock dependencies passed through constructors
  • Type safety: Full TypeScript support for mocked methods
  • Testability: Easy to replace with mocks in tests
  • Abstraction: Business logic doesn't depend on specific ORM implementation details

ORM-Specific Guides​

Each ORM has its own guide with detailed examples:

  • TypeORM - Mocking TypeORM repositories and EntityManager
  • Prisma - Mocking Prisma client instances
  • Drizzle - Mocking Drizzle database instances
  • MikroORM - Mocking MikroORM EntityManager and repositories

Summary​

  • Wrap ORM clients in injectables to make them mockable
  • Create repository classes that encapsulate ORM-specific logic
  • Use Suites to automatically mock repository dependencies
  • Keep repositories focused on data access, not business logic
  • Type everything for full TypeScript support
  • Test error scenarios in addition to happy paths

Next Steps​