sfdpot-exploratory-heuristic

Overview

SFDPOT is James Bach's "San Francisco Depot" heuristic - a catalogue of what can be varied during testing. Published at satisfice.com and in James Bach's testing-curriculum materials.

If HICCUPPS-F (hiccupps-f-heuristic) catalogues what to compare against (oracles), SFDPOT catalogues what to change during exploration. Together they form a complete "how to think about a session" pair.

This skill is a pure reference consumed by testers mid-session.

When to use

• Authoring a charter: pick which SFDPOT dimensions the session should vary.
• Mid-session: tester feels stuck - walk SFDPOT for new ideas of what to vary.
• Bug-bashing: assign different dimensions to different testers so coverage spreads.

How to use

1. Name the target. State the feature or area under test in one line (e.g. "the checkout flow").
2. Walk all six dimensions. For each of S, F, D, P, O, T, ask its prompt from the table below and jot 1-3 concrete variables worth trying. Pull ideas from references/six-dimensions-catalog.md when a dimension feels thin.
3. Fold the picks into a charter. Each dimension's line becomes a mission for the session - see session-based-test-management-reference.
4. Explore, then re-walk when stuck. If ideas dry up mid-session, walk SFDPOT again - a dimension you skipped usually holds the next bug.
5. Interpret with an oracle. For each surprise, reach for HICCUPPS-F (hiccupps-f-heuristic) to decide whether it is actually a bug.

The worked example below applies exactly these steps to a checkout charter.

The six dimensions

SFDPOT names six axes of variation. Pick one or more per session; the full variable catalog for each dimension lives in references/six-dimensions-catalog.md.

Data varies what values; Operations varies how the user moves through. Two dimensions to compose with dedicated tooling: Platform with qa-compatibility for systematic matrix testing, and Time with qa-time for clock-mocking (Tier 2 ROADMAP - not yet shipped).

Worked example - applying SFDPOT to a checkout charter

Charter: "Explore the checkout flow to discover bugs."

Apply SFDPOT to plan the session:

- **S - Structure:** Toggle the `feature-new-checkout=true` flag
  in middle of the session to compare old vs new code paths.
- **F - Function:** Stack multiple promos; combine with gift card;
  combine with store credit. Trigger refund mid-checkout.
- **D - Data:** Cart with 0 items, 1, 100, 1000 items. Cart with
  free items only. Cart with $0.01 total. Cart with $9999.99
  total. Invalid product IDs.
- **P - Platform:** Safari iOS (autofill / Apple Pay), Chrome
  desktop, low-bandwidth Android.
- **O - Operations:** Add, remove, re-add an item. Navigate
  away and return. Refresh during payment processing.
- **T - Time:** Apply a promo that expires in 1 minute, then
  delay 70 seconds. Open two tabs simultaneously and check out
  from each.

This shapes a richer session than "click around the checkout page." Each bullet becomes one mission line in the charter.

SFDPOT vs other heuristics

They're complementary, not competing - a strong session uses multiple. Bach + Bolton's Rapid Software Testing curriculum teaches all of them as a toolkit.

Anti-patterns

Limitations

• Heuristic, not exhaustive. Bugs can hide in dimensions SFDPOT doesn't enumerate (cross-cutting concerns like security, observability) - those have their own heuristic catalogs.
• Requires deliberate practice. A new tester walks SFDPOT mechanically; an experienced one fluently considers each dimension in seconds.
• Variation cost is real. Some dimensions (Platform full matrix; Time clock manipulation) require infrastructure that may not exist for ad-hoc exploration.

References

• Bach J. Heuristics of Software Testability - satisfice.com/heuristics-of-software-testability.
• Bach J. + Bolton M. Rapid Software Testing curriculum - satisfice.com/rapid-software-testing.
• Bolton M. San Francisco Depot - developsense.com.
• Full per-dimension variable catalog: references/six-dimensions-catalog.md.
• Sibling references: hiccupps-f-heuristic, fcc-cuts-vids-heuristic, crusspic-stmpl-heuristic, session-based-test-management-reference, exploratory-tours-reference.