[DeepDev69x3]

Summary of Changes

Closes #2095

Adds comprehensive deterministic unit and integration test coverage for Express request validation middleware in backend/src/middleware/validation.ts, ensuring robust handling of nested schemas, boundary inputs, and consistent 400 response contracts when passed through centralized errorHandler.

Detailed Test Coverage

1. validateBody:

   • Verified clean execution and invocation of next() with no arguments on valid payloads.
   • Verified rejection of missing required fields, capturing z.ZodError.
   • Verified deeply nested schema failures (e.g. nested.details.verified) emitting correct dot-delimited error paths.
   • Verified indexed array element error paths (e.g. tags.1) in structured payloads.
   • Handled boundary inputs (e.g. undefined / empty body) safely without throwing uncaught exceptions.

2. validateQuery & validateParams:

   • Verified string regex matching for pagination parameters (page, limit) and enum validation for query filters.
   • Verified route parameter validation for UUID format invariants (loanId).

3. validate & createSchema Helpers:

   • Verified combined validation across body, query, and params simultaneously.
   • Verified isolated schema generators (createSchema.body, createSchema.query, createSchema.params).

4. Integration with errorHandler (Consistent 400 Contract):

   • Verified HTTP 400 status code on validation errors.
   • Verified legacy format backward compatibility (success: false, message: 'Validation failed', errors: [{ path, message }]`).
   • Verified structured error contract (error.code === 'VALIDATION_ERROR', error.fieldset to first failing field, anderror.detailscontaining complete{ field, message, code }` objects).

Verification

• npm test -- src/middleware/__tests__/validation.test.ts: 15/15 tests passed (100% green).
• npm test: 126/126 test suites passed, 1087/1087 tests passed (0 failed).
• npm run build: tsc -p tsconfig.build.json succeeded with 0 errors.

[github-actions]

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