Exploring case scenarios within a function reliant on the instanceof operator (JEST)

Question

Exploring case scenarios within a function reliant on the instanceof operator (JEST)

Encountering a problem while writing unit tests for a function with instance checks. The business logic is as follows:

let status = new B();
const testFunction = () => {
    if (status instanceof A) {
      console.log('inside A')
    } else if (status instanceof B) {
      console.log('inside B')
    } else {
      console.log('No matchers')
    }

}

Unit Test:

describe('test', ()=>{
  
  it("should test b", ()=>{
    let status = new A()
    expect(status).toBeInstanceOf(A) // passes
    expect(logSpy).toHaveBeenCalledWith('inside A') // fails and expects 'inside B'
  })
})

Believe the test fails because the original file returns an instance of class B for 'status', causing it to match the 'else if' condition instead of the 'if' condition. Unsure how to test this without changing 'status'. Am I missing something?

EDIT: Assuming testFunction() is already invoked in unit tests

javascript unit-testing jestjs

Answer 1

Answer №1

One way to handle this situation is by passing the status as a parameter to your function:

const checkStatus = (status) => {
  if (status instanceof A) {
    console.log('inside A')
  } else if (status instanceof B) {
    console.log('inside B')
  } else {
    console.log('No match found')
  }
}

Then you can call checkStatus() with the specific status you want to test:

const status = new A();
checkStatus(status);

It's important to note that the issue with your test may be due to the function having its own scope. Another potential solution is to mock the variable, although this can be more complex.

Answer 2

One way to handle this situation is by passing the status as a parameter to your function:

const checkStatus = (status) => {
  if (status instanceof A) {
    console.log('inside A')
  } else if (status instanceof B) {
    console.log('inside B')
  } else {
    console.log('No match found')
  }
}

Then you can call checkStatus() with the specific status you want to test:

const status = new A();
checkStatus(status);

It's important to note that the issue with your test may be due to the function having its own scope. Another potential solution is to mock the variable, although this can be more complex.

Exploring case scenarios within a function reliant on the instanceof operator (JEST)

Answer №1

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