High Level Custodian Test Guide

Getting Started With High Level Custodian Test Guide

I ran into this when our QA team was trying to validate custodian API responses across multiple environments. The documentation was scattered across Confluence, Jira, and a half-dead GitHub repo. I put together a practical guide that actually works for people doing this work day to day. Most teams approach this wrong by trying to cover every edge case upfront. That burns weeks. The better path is to validate the happy path first, then systematically expand coverage based on where your actual integration points break. Here's how I structure it:

1. Identify your custodian providers and their API versions - Don't assume they're all on the same schema. I once spent three days debugging a type mismatch that turned out to be a custodian silently rolling out v2 endpoints while keeping v1 documented. Cross-reference the actual response payloads against what your test suite expects. Check the last modification dates on their API docs. 2. Map the core test objects - Account creation, position lookup, trade confirmation, settlement status. These are your anchors. Everything else branches from them. If you can't reproduce a position lookup end-to-end, nothing downstream matters. 3. Build a baseline script, not a framework - I've seen teams spend two sprints building a "flexible" test framework for this. Just write a single Python script with hardcoded credentials and test each flow sequentially. Use environment variables for secrets. Run it manually for a week. Once you know which endpoints actually fail, THEN invest in a proper framework. This saved me about 40 hours on my last engagement.

4. Mock the unhappy paths separately - Network timeouts, 401s, malformed responses. Use a proxy like mitmproxy or WireMock to inject these. Don't rely on your custodian's sandbox to reproduce every error condition - most of them don't surface edge cases properly. 5. Data parity check - Your test account positions should reconcile with what's in production at a snapshot point in time. I discovered a sync delay of 4-6 hours between the custodian's reporting endpoint and their transactional API. If your tests run immediately after a trade, they'll fail even when everything is working correctly. Build in a polling mechanism with a configurable wait window.

Common Pitfalls

The biggest one I see is assuming idempotency where it doesn't exist. Some custodian APIs will create duplicate positions if you replay a request, others will silently return the existing record. Check this before your automated runs start creating garbage data in your test environment. Another thing: timezone handling. A few custodians return timestamps in UTC, others use the account's configured timezone. One team missed this and their end-of-day reconciliation was always off by six hours because the custodian was in London time and the reporting dashboard defaulted to EST.

What This Guide Covers

Setup and configuration, test object mapping, script structure, mock strategies, data reconciliation, and common failure modes. I'll link to the full version below. High Level Custodian Test Guide - Full Document

When It Doesn't Work

Don't try to test custodian behavior itself - test your integration with the custodian. You can't validate whether their settlement engine works correctly. You can only verify that your system handles their responses as expected. Trying to do the former will waste months and get you nowhere. If your custodian doesn't have a proper sandbox environment, negotiate access to a staging account with synthetic data. I've seen teams try to test against production with dummy accounts and it never ends well. Compliance will notice, and they won't be happy. The guide is a living document. Update it whenever a custodian changes their API without updating their docs - which is basically every quarter. I keep a changelog in the repo and flag breaking changes in red at the top of the relevant sections.