migrate test helpers to typescript (reduxjs#3515)

Former-commit-id: 82d5a48
Former-commit-id: a06f235

Author: cellog

test/helpers/actionCreators.js.REMOVED.git-id

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+46964ea9cef1aec64487cde982fc7450877410d7

test/helpers/actionCreators.ts.REMOVED.git-id

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+import { MiddlewareAPI, Dispatch, AnyAction } from '../..'
+
+type ThunkAction<T extends any = any> = T extends AnyAction
+  ? AnyAction
+  : T extends Function
+  ? T
+  : never
+
+export function thunk({ dispatch, getState }: MiddlewareAPI) {
+  return (next: Dispatch) => <T>(action: ThunkAction) =>
+    typeof action === 'function' ? action(dispatch, getState) : next(action)
+}

test/helpers/actionTypes.js renamed to test/helpers/actionTypes.ts

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+c10d3d017ed4b5122d25d5ed2b80309ccadf7cf9