app-api-contract-testing

Cross-App API Contract Testing

When this app calls another app via Gate AppApisApi.callAppApi(...), it becomes a consumer that depends on the provider operation behaving a certain way. A contract captures that expectation. Contracts are authored and validated locally, then verified centrally (public-api → Gate runs the real provider call) — there is no local runtime verification command.

A contract is identified by providerAppId + operationId — the business contract is the provider operation, not the HTTP transport.

When to do this (during app development)

• After adding or changing a callAppApi(...) dependency in runtime code.
• Before relying on a provider, or after a provider you depend on is upgraded (run verify-consumer).
• Before shipping a change to an app other apps call (run verify-provider to catch every dependent consumer org-wide).

Prerequisites

• fusebase auth --api-key=<id>.<key> (an API key is required).
• orgId/productId in fusebase.json, and the app configured with a path.
• The cross-app-api-calls-analysis flag (already enabled — this skill is only present when it is).

Workflow

# 1. Discover dependencies — scans runtime TS for callAppApi(...) and writes
#    fusebaseAppApiDependenciesMeta into fusebase.json
fusebase analyze app-apis --feature <appId>

# 2. Scaffold draft contracts from the resolved callsites
fusebase app-api-contracts scaffold --app <appId>
#    → drafts are bare { "expect": { "status": 200 } } with input inferred from
#      the call payload. EDIT them into real assertions (see "Contract files").
#    Existing *.contract.json files are SKIPPED (your edits are safe); only missing
#    ones are created. Pass --force to overwrite existing files back to fresh
#    drafts (discards your edits).

# 3. Validate offline — structure + that each contract maps to a real dependency.
#    No provider call.
fusebase app-api-contracts validate --app <appId>

# 4. Publish the validated set to central storage (full replacement, idempotent;
#    aborts and uploads nothing if any contract is invalid)
fusebase app-api-contracts publish --app <appId>

# 5. Verify centrally against the live provider
fusebase app-api-contracts verify-consumer --app <appId>          # this app's contracts
fusebase app-api-contracts verify-provider --app <providerAppId>  # org-wide inbound check

Review and complete every draft (required, not optional)

Scaffolding is a starting point, not a finished contract. It seeds only the request side (input, inferred from the call payload). The response assertion is NOT generated — each draft gets only expect.status: 200, never an expect.body or expect.error. An unedited draft therefore asserts almost nothing (just "the call returned 200").

So after every scaffold, open each generated *.contract.json and edit it to match what this app actually relies on:

• Define expect by hand — add expect.body matchers for the response fields the app reads, and add the error cases the app handles (expect.status + expect.error for the 4xx/5xx paths). This is the core of the contract and is never produced by scaffolding.
• Check input — fix or complete the inferred payload if it doesn't reflect a real call the app makes (and add cases for other meaningful inputs).
• Rename cases — give each case.name a meaningful description of the scenario.
• Remove any scaffolded contract for a dependency the app doesn't truly depend on.

Treat a scaffolded-but-unreviewed contract as incomplete: validate/publish/verify only after the expect blocks express the app's real expectations.

Key rule: verify-* read the published set, not local files. After editing a contract, re-run publish before verifying — otherwise the old published version is tested.

Add --json to validate / verify-consumer / verify-provider for CI: a single JSON document with a top-level ok flag mirroring the exit code. publish is an action, not a check — branch on its exit code.

Dynamic (unresolved) calls

When callAppApi(...) is dynamic and static analysis cannot resolve the target, declare it by hand, then scaffold that one:

fusebase app-api-contracts unresolved --app <appId>
fusebase app-api-contracts add-manual-dependency --app <appId> --provider <providerAppId> --operation <operationId>
fusebase app-api-contracts scaffold --app <appId> --provider <providerAppId> --operation <operationId> --force

Contract files

Discovered under <app-path>/contracts/app-apis/<providerAppId>/<operationId>.contract.json:

{
  "kind": "app-api-consumer-contract",
  "schemaVersion": "2026-06-03",
  "providerAppId": "<provider app id>",
  "operationId": "listTasks",
  "cases": [
    {
      "name": "lists open tasks",
      "input":  { "query": { "status": "open" } },
      "expect": { "status": 200, "body": { "tasks": [ { "id": { "$matcher": "string" } } ] } }
    }
  ]
}

• input → the Gate request envelope (path/query/body); omit to send {}. input is sent, not asserted. A matcher left in input is synthesized into a concrete sample before the call ({"$matcher":"string"} → "contract-draft", number → 1, enum → first $value, $optional → omitted). Scaffolding may seed a matcher for a value it couldn't read from your code (e.g. a dynamic path id) — the synthesized sample is almost certainly not a real record, so replace input placeholders with real values before publish. Matchers are meaningful only in expect.
• expect.status is required; expect.body and expect.error are optional. expect.error matches data.error on non-2xx responses.
• Matchers (type-only): {"$matcher":"string"|"number"|"boolean"}, {"$matcher":"enum","$value":[...]}. Add "$optional":true to allow absence, "$nullable":true to allow an explicit null (combinable). Plain JSON = exact match; objects match partially (only listed keys checked); a length-1 array [ X ] matches every element (so a nullable element needs [{"$matcher":"string","$nullable":true}]), a length-N array expects exactly N positional elements.
• Not supported (ignored-with-warning if seen in the provider schema): regex, ranges/lengths, formats (date/uuid/email), oneOf/anyOf/allOf.

When the provider publishes a manifest, verification also checks responses against its OpenAPI schema automatically — even a bare { "status": 200 } draft gets that check. Missing manifest / unsupported keywords surface as warnings, never failures.

Notes

• Verification runs the real provider handler, so it can cause side effects (writes, emails). There is no fixture/sandbox environment.
• verify-provider runs every targeting consumer's contracts as the triggering user; it is org-wide (sees consumers beyond the local fusebase.json).