test: integrate prisma-mock for unit tests

docs/testing-with-prisma-mock.md

@@ -0,0 +1,130 @@
+# Testing with Prisma Mock
+
+This document describes how `prisma-mock` is integrated into the JabRefOnline test suite.
+
+## Overview
+
+We use [`prisma-mock`](https://github.com/demonsters/prisma-mock) for mocking the Prisma database client in tests. This provides fast, isolated tests without requiring a real PostgreSQL database connection.
+
+## Current Implementation
+
+### Unit Tests ✅
+
+**Status:** Fully implemented and working
+
+Unit tests now use `prisma-mock` to create in-memory mock databases:
+
+- **`server/journals/journal.service.spec.ts`** - Tests journal service with mocked data
+- **`server/documents/user.document.service.spec.ts`** - Tests document service with mocked data
+
+#### Key Features
+
+1. **DMMF Generator**: We use a Prisma generator to export the database schema (DMMF - Data Model Meta Format) which is required by prisma-mock:
+
+   ```prisma
+   generator prismaMock {
+     provider = "node /home/runner/work/JabRefOnline/JabRefOnline/node_modules/prisma-mock/prisma-dmmf-generator.mjs"
+     output = "./generated/dmmf.ts"
+   }
+   ```
+
+2. **Test Setup Pattern**:
+
+   ```typescript
+   import createPrismaMock from 'prisma-mock/client'
+   import { mockDeep } from 'vitest-mock-extended'
+   import { Prisma, type PrismaClient } from '../database'
+   import * as dmmf from '../database/generated/dmmf'
+
+   let prisma: PrismaClient
+
+   beforeEach(() => {
+     const mockClient = mockDeep<PrismaClient>()
+     prisma = createPrismaMock(Prisma, {
+       mockClient,
+       datamodel: { enums: dmmf.enums, models: dmmf.models },
+     })
+     register('PrismaClient', { useValue: prisma })
+   })
+   ```
+
+3. **Data Seeding**: Tests seed their own data using standard Prisma create operations:
+   ```typescript
+   await prisma.journal.create({ data: testJournal })
+   ```
+
+#### Benefits
+
+- ⚡ **Fast**: No database I/O - tests run in milliseconds
+- 🔒 **Isolated**: Each test gets a fresh mock database
+- 🚀 **Simple**: No database setup or teardown required
+- 🎯 **Focused**: Tests only what they need to test
+
+### Integration Tests
+
+**Status:** Still using real PostgreSQL database
+
+Integration tests continue to use a real PostgreSQL database because they:
+
+1. Test complex GraphQL queries with nested includes and relationships
+2. Validate the full stack integration including actual database behavior
+3. Require features that are not fully supported by prisma-mock yet
+
+**Rationale:** Integration tests are meant to test the integration between components with real dependencies. Using a real database here is appropriate and aligns with integration testing best practices.
+
+## Running Tests
+
+```bash
+# Run unit tests (uses prisma-mock)
+pnpm test:unit
+
+# Run integration tests (uses real PostgreSQL)
+pnpm test:integration
+
+# Run all tests
+pnpm test
+```
+
+## Future Improvements
+
+Potential areas for future work:
+
+1. **Expand prisma-mock coverage**: As prisma-mock evolves and adds support for more complex query patterns, we could migrate more tests to use it.
+
+2. **Hybrid approach for integration tests**: Some simpler integration tests could potentially use prisma-mock while keeping complex ones on real database.
+
+3. **Custom mock implementations**: For specific use cases not supported by prisma-mock, we could create custom mock implementations.
+
+## Generating DMMF
+
+The DMMF (datamodel) is automatically generated when you run:
+
+```bash
+pnpm prisma:generate
+```
+
+This creates `server/database/generated/dmmf.ts` which contains the schema information needed by prisma-mock.
+
+## Troubleshooting
+
+### DMMF Generator Fails
+
+If the Prisma generator fails, ensure the path to the generator is correct in `server/database/schema.prisma`. The path should be absolute as Prisma executes generators from different working directories.
+
+### Tests Fail with Type Errors
+
+Make sure to regenerate the Prisma client and DMMF after schema changes:
+
+```bash
+pnpm prisma:generate
+```
+
+### Mock Data Not Persisting
+
+Remember that each `beforeEach` creates a fresh mock instance. If you need data to persist across tests within a suite, create the mock in `beforeAll` instead (though this is generally not recommended).
+
+## References
+
+- [prisma-mock GitHub Repository](https://github.com/demonsters/prisma-mock)
+- [prisma-mock Documentation](https://github.com/demonsters/prisma-mock#readme)
+- [Prisma Documentation](https://www.prisma.io/docs/)

package.json

@@ -140,6 +140,7 @@
     "prettier": "3.6.2",
     "prettier-plugin-organize-imports": "4.3.0",
     "prisma": "6.15.0",
+    "prisma-mock": "^1.0.0",
     "storybook": "10.0.4",
     "storybook-vue-addon": "0.6.3",
     "tailwindcss": "^4.1.17",