init create-react-hook@2.6.18

src/index.tsx

@@ -0,0 +1,23 @@
+import * as React from 'react';
+
+export const useMyHook = () => {
+  let [{
+    counter
+  }, setState] = React.useState<{
+    counter: number;
+  }>({
+    counter: 0
+  });
+
+  React.useEffect(() => {
+    let interval = window.setInterval(() => {
+      counter++;
+      setState({counter})
+    }, 1000)
+    return () => {
+      window.clearInterval(interval);
+    };
+  }, []);
+
+  return counter;
+};

src/react-app-env.d.ts

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+/// <reference types="react-scripts" />

src/test.ts

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+import { useMyHook } from './'
+
+describe('useMyHook', () => {
+  it('is truthy', () => {
+    expect(useMyHook).toBeTruthy()
+  })
+})