also handle optional arguments

Author: phryneas

src/__tests__/renderHookToSnapshotStream.test.tsx

@@ -109,4 +109,14 @@ test.skip('type test: render function without an argument -> no argument require
     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

@@ -41,10 +41,20 @@ 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
 }
 
+/**
+ * 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> = {},