src/__tests__/renderHookToSnapshotStream.test.tsx

@@ -3,7 +3,10 @@
 import {EventEmitter} from 'node:events'
 import {scheduler} from 'node:timers/promises'
 import {test, expect} from '@jest/globals'
-import {renderHookToSnapshotStream} from '@testing-library/react-render-stream'
+import {
+  renderHookToSnapshotStream,
+  SnapshotStream,
+} from '@testing-library/react-render-stream'
 import * as React from 'react'
 
 const testEvents = new EventEmitter<{
@@ -72,3 +75,48 @@ test.each<[type: string, initialValue: unknown, ...nextValues: unknown[]]>([
     expect(await takeSnapshot()).toBe(nextValue)
   }
 })
+
+test.skip('type test: render function without an argument -> no argument required for `rerender`', async () => {
+  {
+    // prop type has nothing to infer on - defaults to `void`
+    const stream = await renderHookToSnapshotStream(() => {})
+    const _test1: SnapshotStream<void, void> = stream
+    // @ts-expect-error should not be assignable
+    const _test2: SnapshotStream<void, string> = stream
+    await stream.rerender()
+    // @ts-expect-error invalid argument
+    await stream.rerender('foo')
+  }
+  {
+    // prop type is implicitly set via the render function argument
+    const stream = await renderHookToSnapshotStream((_arg1: string) => {})
+    // @ts-expect-error should not be assignable
+    const _test1: SnapshotStream<void, void> = stream
+    const _test2: SnapshotStream<void, string> = stream
+    // @ts-expect-error missing argument
+    await stream.rerender()
+    await stream.rerender('foo')
+  }
+  {
+    // prop type is implicitly set via the initialProps argument
+    const stream = await renderHookToSnapshotStream(() => {}, {
+      initialProps: 'initial',
+    })
+    // @ts-expect-error should not be assignable
+    const _test1: SnapshotStream<void, void> = stream
+    const _test2: SnapshotStream<void, string> = stream
+    // @ts-expect-error missing argument
+    await stream.rerender()
+    await stream.rerender('foo')
+  }
+  {
+    // argument is optional
+    const stream = await renderHookToSnapshotStream((_arg1?: string) => {})
+
+    const _test1: SnapshotStream<void, void> = stream
+    const _test2: SnapshotStream<void, string> = stream
+    const _test3: SnapshotStream<void, string | undefined> = stream
+    await stream.rerender()
+    await stream.rerender('foo')
+  }
+})

src/renderHookToSnapshotStream.tsx

@@ -41,11 +41,21 @@ export interface SnapshotStream<Snapshot, Props> extends Assertable {
    * Does not advance the render iterator.
    */
   waitForNextSnapshot(options?: NextRenderOptions): Promise<Snapshot>
-  rerender: (rerenderCallbackProps: Props) => Promise<void>
+  rerender: (rerenderCallbackProps: VoidOptionalArg<Props>) => Promise<void>
   unmount: () => void
 }
 
-export async function renderHookToSnapshotStream<ReturnValue, Props>(
+/**
+ * if `Arg` can be `undefined`, replace it with `void` to make type represent an optional argument in a function argument position
+ */
+type VoidOptionalArg<Arg> = Arg extends any // distribute members of a potential `Props` union
+  ? undefined extends Arg
+    ? // eslint-disable-next-line @typescript-eslint/no-invalid-void-type
+      void
+    : Arg
+  : Arg
+
+export async function renderHookToSnapshotStream<ReturnValue, Props = void>(
   renderCallback: (props: Props) => ReturnValue,
   {initialProps, ...renderOptions}: RenderHookOptions<Props> = {},
 ): Promise<SnapshotStream<ReturnValue, Props>> {
@@ -61,8 +71,9 @@ export async function renderHookToSnapshotStream<ReturnValue, Props>(
     renderOptions,
   )
 
-  function rerender(rerenderCallbackProps: Props) {
-    return baseRerender(<HookComponent arg={rerenderCallbackProps} />)
+  function rerender(rerenderCallbackProps: VoidOptionalArg<Props>) {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+    return baseRerender(<HookComponent arg={rerenderCallbackProps as any} />)
   }
 
   return {