Testing and Overrides

Use .override() when tests need to replace an existing registration with a mock.

function buildContainer() {
  return new Container()
    .registerClass('logger', ConsoleLogger, [])
    .registerClass('db', PgDb, [])
    .registerClass('users', UserRepo, ['logger', 'db'])
}

const c = buildContainer()
  .override('logger', mockLogger)
  .override('db', mockDb)

The override value must be assignable to the original registered type. Missing keys and incompatible mocks are TypeScript errors.

Override Timing

Overrides must happen before the key is resolved:

const logger = c.get('logger')
c.override('logger', mockLogger)

That second line throws. A late override would split the graph: existing consumers would hold the old instance while later resolves returned the mock.

Ownership

Override values are externally owned. Like registerValue, an override is not added to the container's disposal queue. The test fixture owns its cleanup.

Scope Locality

An override mutates only the container it is called on:

const scope = root.createScope().override('db', mockDb)

The root and sibling scopes are unchanged. Parent-level overrides are visible through the usual parent lookup.