JS/TS: how to mock internal functions?

sal3jfc 0
Viewed 25

I am trying to run through some basic tests to make sure my coverage is adequate.

my class

class Foo {
  constructor(host) {}

  getUserPrivileges() {
    const response = this.host.fetch('myurl');
    const data = await response.json();

    return data.privilege //string
  }

  getInfo(userPrivilegeType: string) {
       const response  = this.host.fetch('myurl/${userPrivilegeType}');
       const data = await response.json();

       return data;
  }

  mainFunction() {

     const userPrivilegeType = await getUserPrivileges();  // return "free" or "paid"

     const data = await getInfo(userPrivilegeType);  // returns an object or null

     let name = "not specified"; 

     if (data) {
        name = data.name;
     }

     return "Finished with " + name;
  }

}

if I wanted to run a test for mainFunction() that it returns a value, how can I mock the inside functions but not mock mainFunction so that it actually triggers it? I want the function coverage to increase but obviously don't want to make real API fetches to a server.

chai mocha.js typescript
1 Answers

In this case you would mock host.

const host = makeWhateverHostIs()
jest.spyOn(host, 'fetch').mockImplementation(url => {
  if (url === 'myurl') return { some: 'data' }
  if (url === 'myurl/admin') return { some: 'other data' }
})

const foo = new Foo(host)
Alex Wayne0
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