Using partial shape for unit testing with typescript

Question

Let's say i want to unit test a function in typescript. This function use an "option" type (object) parameter with a complex shape.

interface option {
  param1 : string
  param2 : number
  param3 : { 
    param4 : string
    param5 : boolean
    }
  .
  .
  .
  param15 : string
}

const functionToTest = (opt:option)=>{
   ...do stuff with option
}

Now let say i want to write a unit test that mimic the correct behaviour of functionToTest when param1 change, ignoring the other parameter that have no influence on the result.

It's my understanding that to make my test more resilient, i can just write in plain JS

const option1 = {
  param1 : "foo"
}

and do my testing

expect(functionToTest(option1)).to.be.true;

However, if i write my test with typescript, i will have to write a full option1 object with all of the interface (dummy) members, althought most will be ignored, and it will divert the reader from the true goal of the test.

Are there workarounds around this or something i should change in my thinking ?

Answer 1

You can take advantage of typescript's Partial for this.

interface YourInterface {
  prop: string;
  foo: number;
}

const data: Partial<YourInterface> = {   
   prop: 'value'
};

// service is an instance of SomeService
service.sendData(<YourInterface> data);

class SomeService {
  sendData(data: YourInterface) {

  }
}

Answer 2

In my tests, I use the as type assertion to pass in partial objects to a function.

const options = {
   param1: 'param1',
   param2: 22 
} as Option;

expect(functionToTest(options)).to.be.true;