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JavaScript JavaScript Unit Testing Improving Our Tests Catching an Error

Santiago Cabrera
Santiago Cabrera
11,087 Points
Posted by Santiago Cabrera
Santiago Cabrera
11,087 Points

Don't understand why it doesn't work

Nothing

subtraction_spec.js 
var expect = require('chai').expect

describe('subtraction', function () {
  var subtraction = require('../WHEREVER')  
  it('only works with numbers', function () {
    // YOUR CODE HERE
    expect(subtraction.subtraction()).to.throw(Error);
  })
})
subtraction.js 
function subtraction (number1, number2) {
  if (typeof number1 !== 'number' || typeof number2 !== 'number') {
    throw Error('subtraction only works with numbers!')
  }
  return number1 - number2
}

1 Answer

Tim Gavlick
Tim Gavlick
11,725 Points
Tim Gavlick
Tim Gavlick
11,725 Points

2 things:

  1. We apparently don't need to call "subtraction.subtraction()". "subtraction()" works just fine.

  2. expect, in this case, is looking for a callable function and not the result of calling the function.

expect(subtraction('a', 'b'))

won't give Chai the chance to catch the exception, but giving it a callable function will. This can be done via the wrapper method in the previous video, or by passing a bound or anonymous function into expect; e.g.

expect(subtraction.bind(null, 'a', 'b'))