這一篇的測試比較偏專屬 React 的 Redux Toolkit 測試，如果沒有使用 Redux 的話，可以跳過這一篇～

程式碼

以 TodoList 為例，會有一個 todoSlice，裡面有 addTodo、removeTodo、toggleTodo 三個 action，我們會測試這三個 action 是否正常運作。

export const todoSlice = createSlice({
  name: "todo",
  initialState,
  reducers: {
    addTodo: (state, action: PayloadAction<string>) => {
      state.todoList.push({
        title: action.payload,
        id: Math.random(),
        isDone: false,
      });
    },
    removeTodo: (state, action: PayloadAction<number>) => {
      state.todoList = state.todoList.filter(
        (todo) => todo.id !== action.payload
      );
    },
    toggleTodo: (state, action: PayloadAction<number>) => {
      state.todoList = state.todoList.map((todo) =>
        todo.id === action.payload ? { ...todo, isDone: !todo.isDone } : todo
      );
    },
  },
});

TodoPage 則會使用 useSelector 取得 todoList，並且使用 useDispatch 去呼叫 action。

import { addTodo, removeTodo, toggleTodo } from "@/store/todo";
import useAppDispatch from "@/utils/hooks/useAppDispatch";
import useAppSelector from "@/utils/hooks/useAppSelector";
import { useState } from "react";
import styled from "./index.module.scss";

export const TodoPage = () => {
  const todoList = useAppSelector((state) => state.todo.todoList);
  const dispatch = useAppDispatch();

  const [todo, setTodo] = useState("");

  const addTodoHandler = () => {
    dispatch(addTodo(todo));
    setTodo("");
  };

  return (
    <div className={styled.container}>
      <input
        type='text'
        value={todo}
        onChange={(e) => setTodo(e.target.value)}
      />
      <button onClick={addTodoHandler}>ADD</button>
      {todoList.map((todo) => (
        <li
          key={todo.id}
          className={
            todo.isDone ? `${styled.todo} ${styled.done}` : styled.todo
          }
          onClick={() => dispatch(toggleTodo(todo.id))}
        >
          <input type='checkbox' checked={todo.isDone} readOnly />
          <span>{todo.title}</span>
          <button onClick={() => dispatch(removeTodo(todo.id))}> remove</button>
        </li>
      ))}
    </div>
  );
};

在測試時，就會分別就這兩個部分進行測試。

redux toolkit 測試

import todoSlice, { TodoState, addTodo, removeTodo, toggleTodo } from "./todo";

describe("todoSlice", () => {
  let initialState: { todoList: TodoState[] };
  const todo1 = { id: 1, title: "Test Todo 1", isDone: false };
  const todo2 = { id: 2, title: "Test Todo 2", isDone: false };
  const todo3 = { id: 3, title: "Test Todo 3", isDone: false };
  const state = { todoList: [todo1, todo2, todo3] };

  beforeEach(() => {
    initialState = { todoList: [] };
  });

  it("當 addTodo 函式輸入 'Test Todo' todoList 新增一項 todo title 為 Test Todo 且 isDone 為 false", () => {
    const actual = todoSlice.reducer(initialState, addTodo("Test Todo"));
    expect(actual.todoList.length).toEqual(1);
    expect(actual.todoList[0].title).toEqual("Test Todo");
    expect(actual.todoList[0].isDone).toEqual(false);
  });

  it("當 removeTodo 函式輸入 2 則只移除 id 為 2 的 todo", () => {
    const actual = todoSlice.reducer(state, removeTodo(2));
    expect(actual.todoList.length).toEqual(2);
    expect(actual.todoList).toContain(todo1);
    expect(actual.todoList).toContain(todo3);
    expect(actual.todoList).not.toContain(todo2);
  });

  it("當 toggleTodo 函式輸入 2 則 id 為 2 的 todo isDone 為 true", () => {
    const actual = todoSlice.reducer(state, toggleTodo(2));
    expect(actual.todoList[1].isDone).toEqual(true);
  });
});

依據不同情況給入相對應的初始值，並且測試是否有正確的回傳值。

TodoPage 測試

import { render, screen } from "@testing-library/react";
import { Provider } from "react-redux";
import { store } from "@/store";
import { TodoPage } from ".";
import userEvent from "@testing-library/user-event";

describe("TodoPage", () => {
  const user = userEvent.setup();
  beforeEach(() => {
    render(
      <Provider store={store}>
        <TodoPage />
      </Provider>
    );
  });

  it("當輸入「New Todo」並點擊 add 按鈕，顯示「New Todo」文字", async () => {
    const inputElement = screen.getByRole("textbox");
    const addButtonElement = screen.getByRole("button", { name: /add/i });

    await user.type(inputElement, "New Todo");
    await user.click(addButtonElement);

    const todoElement = screen.getByText("New Todo");
    expect(todoElement).toBeInTheDocument();
  });

  it("當點擊「New Todo」文字，checkbox 會被勾選", async () => {
    const todoElement = screen.getByText("New Todo");
    await user.click(todoElement);

    const checkboxElement = screen.getByRole("checkbox");
    expect(checkboxElement).toBeChecked();
  });

  it("當點擊 remove 按鈕，'New Todo' 文字不會顯示", async () => {
    const removeButtonElement = screen.getByRole("button", { name: /remove/i });
    await user.click(removeButtonElement);

    const todoElement = screen.queryByText("New Todo");
    expect(todoElement).not.toBeInTheDocument();
  });
});

TodoPage 就會是測試使用者操作的部分，是否有正確的 UI 顯示、勾選、移除等等。

總結

Redux toolkit 的測試乍聽之下好像很難測，不過因為 redux 就是各種函式統一管理，所以測試起來也不會太難，就像是一般的函式測試，只不過要依據不同的情況給入不同的初始值，才能測試出不同的結果。