---
title: Test against the seam
description: Drive the real services with in-memory fakes, render UI against a recording transport, and check your own implementations with the conformance runners.
sidebar:
  label: Testing
seo:
  title: Test a DomainKit integration
---

`domainkit/testing` exists so host tests never stub global `fetch`. Every fake is a real
implementation of a seam the lifecycle already goes through, so the code under test is the code that
ships.

## A fake provider

<Snippet
  file="examples/testing/fakes.ts"
  region="provider"
  title="A provider over in-memory zones"
/>

Seed `records` to produce `Noop` and `Conflict` operations, set `failWrite` to exercise a partial
receipt, and set `oauth` to add the interactive method beside the token one.

<Snippet file="examples/testing/fakes.ts" region="failures" title="Failing one write" />

## One layer for the lifecycle

<Snippet file="examples/testing/fakes.ts" region="layer" title="Memory storage and a fake pool" />

<Snippet file="examples/testing/fakes.ts" region="run" title="Driving the real services" />

`DomainKit.layerMemory` adds `Storage.layerMemory` and a throwaway custody key, so a test needs no
database and no key material.

:::caution
`Testing.provider` registers its zones in one table shared by the whole process, and
`Testing.resolver()` answers from that table. Give each test its own zone, or a record another test
applied will answer a public DNS query here.
:::

## Public DNS answers

<Snippet file="examples/testing/fakes.ts" region="resolver" title="An explicit answer table" />

Passing a table replaces the fake providers' zones entirely, which is how you test a requirement
that is satisfied at the provider and still missing in public DNS.

## UI tests

<Snippet file="examples/testing/fakes.ts" region="transport" title="A transport for the browser" />

`Testing.transport` mounts `domainkit/server` over memory storage and a fake provider, then points
`Transport.fromFetch` at that handler. Rendering `<DomainKit.Root transport={transport}>` gives a
component tree that connects, plans, approves, applies, observes, and cleans up for real.

`transport.calls` records `{ method, input }` for every call, so a test can assert that approving
sent the operation ids the customer selected. Declaring fewer capabilities renders the UI against a
host that mounted only part of the route group.

## Conformance

<Snippet file="examples/testing/conformance.ts" region="storage" title="Your own Storage" />

<Snippet file="examples/testing/conformance.ts" region="provider" title="Your own provider" />

The storage runner takes a layer and registers one case per invariant with your test runner. The
provider runner writes to a real account and cleans up after itself, so it belongs in an opt-in
suite rather than in CI.

The [`domainkit/testing` reference](/docs/reference/testing) lists every fake and its options.