Testing NoSQL Repositories

In this lesson, you will learn how to create flexible test fixtures that account for the polymorphic nature of NoSQL document structures.

When testing a NoSQL repository, you cannot rely on the rigid, uniform rows found in SQL databases. Because NoSQL documents often contain optional fields, nested arrays, or evolving schemas, your test data (fixtures) must reflect this real-world variability to ensure your repository methods remain robust.

Embracing Document Flexibility

A "fixture" is essentially a mock document that represents a state of your database. Since NoSQL documents are flexible, you should design your test suite to handle three primary variations:

1. The Minimal Document: Contains only mandatory fields.
2. The "Fat" Document: Contains every possible optional field or large nested array.
3. The Evolving Document: A document that mimics a different schema version to ensure your code handles legacy or future formats correctly.

Example: Polymorphic Fixtures

Imagine you are testing a ProductRepository. Some products might have a price field, while others might use an offers array. Your test fixture logic should allow you to inject these variations easily:

// Test fixture factory
const createProduct = (overrides = {}) => ({
  name: 'Sample Item',
  category: 'Electronics',
  tags: ['sale'],
  ...overrides // Allows injecting or omitting fields for specific test cases
});

// Test case for a document with optional nested data
it('should fetch products even when the "specs" object is missing', async () => {
  const minimalProduct = createProduct({ specs: undefined });
  await repository.save(minimalProduct);
  
  const result = await repository.findById(minimalProduct.id);
  expect(result.specs).toBeUndefined();
});

By creating a factory function rather than static JSON files, you gain the ability to generate documents that test the "boundaries" of your schema. This ensures that your repository logic—such as data mapping or aggregation—doesn't crash when it encounters an unexpected document structure. Always test for the absence of fields as aggressively as you test for their presence.

Key Takeaway: Since NoSQL documents allow for schema variation, use dynamic fixture factories to test how your repository handles minimal, exhaustive, and incomplete data structures.