added typescript test for act export

Author: mpeyper

Diff for: test/typescript/act.ts

@@ -0,0 +1,11 @@
+import { act } from '@testing-library/react-hooks'
+
+function checkTypesWithUndefinedResult() {
+  const callback = () => undefined;
+  act(callback)
+}
+
+function checkTypesWithVoidResult() {
+  const callback = () => {};
+  act(callback)
+}