cra-template-jam/template/src/features/counter/counterSlice.spec.ts

A quick start Create React App template with React Router, Redux Toolkit, TypeScript, Styled Components and custom ESlint configurations

import counterReducer, {
    CounterState,
    increment,
    decrement,
    incrementByAmount,
} from './counterSlice';

describe('counter reducer', () => {
    const initialState: CounterState = {
        value: 3,
        status: 'idle',
    };

    it('should handle initial state', () => {
        expect(counterReducer(undefined, { type: 'unknown' })).toEqual({
            value: 0,
            status: 'idle',
        });
    });

    it('should handle increment', () => {
        const actual = counterReducer(initialState, increment());

        expect(actual.value).toEqual(4);
    });

    it('should handle decrement', () => {
        const actual = counterReducer(initialState, decrement());

        expect(actual.value).toEqual(2);
    });

    it('should handle incrementByAmount', () => {
        const actual = counterReducer(initialState, incrementByAmount(2));

        expect(actual.value).toEqual(5);
    });
});