Kerangka kerja pengujian unit javascript

// Run in console: npm install --save-dev jest

const myMockFunc = jest.fn(); 
console.log(myMockFunc()); 
// > undefined 
 
myMock.mockReturnValueOnce(false).mockReturnValue(true); 
 
console.log(myMock(), myMock(), myMock()); 
// > false, true, true
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