Check JS Foundations for impure functions

[wvmitchell]

Description

In seeing students solve the current (new) JS foundations, some of the tests cannot be passed without creating an impure function. None of the tests should require this.

Summary of Changes

• Solve all the existing JS foundations, looking for spaces where the test cannot be solved without creating an impure function
• Refactor/replace any tests that require the creation of an impure function

Notes

• Testing for the side effect of a function is an example of this. If you encounter a test where it is expected that something has changed as the result of running a function, but that function didn't return anything, it's a side effect, and needs to go away.
• This issue will require changes to the JS Foundations repo, even tho the issue is linked to front-end-curriculum. Please make sure to make your PR there, and link the PR in a comment below.

[kaylagordon]

An example is in spa tests:

 it.skip('should rack up a bill', function(){
    var nik = createCustomer('Nik', 0 , [])
    var footMassage = createService('foot massage', 65)
    var facial = createService('facial', 50)
    var nikFootMassage = bookServices(nik, footMassage)
    var nikFacial = bookServices(nik, facial)

    assert.deepEqual(nikFootMassage.bookings, ['foot massage','facial'])
    assert.deepEqual(nikFacial.bill, 115)
  })

Where you'd have to push the service into nik when bookServices is invoked in order for nikFootMassage and nikFacial to be connected.

[sertmer]

Notes for me: I'm also going to be keeping an eye on on wether or not to put them in any order. Might also fix some things like mis-named tests, confusing themes (vhs), file names

[sertmer]

Here's the PR for these changes :)

https://github.com/turingschool-examples/javascript-foundations/pull/115