Possible issue in unit test on Lens Person exercise

Programming JavaScript
1

Hi,

In the tests for nameLens on the Lens Person exercise, I think there may be an issue.

The test for ensuring immutability expects that the test data person object’s name should not equal “Sara Lakshamanan”.

I think there are several issues causing this test to always pass.

First, it only applies to the “forename” test, where the lens is used to set a new name of “Sara Lakshmanan”. This test doesn’t make sense at all if the “surname” test is not skipped, since in an “incorrect” solution, where the object is mutated, it would then equal “Saravanan Laksh”.

The other issue is that: “Lakshamanan” and “Lakshmanan” are not equal, so even with skipping the “surname” test, this test will always pass.
There is a second typo issue in the streetLens, since “street” and “Street” are not equal.

The first issue doesn’t apply to the other test groups, as they only have one .set test, however I think it would still be better to replace each of these with a test positively checking the specific property of person, or the full expected object:

  • expect(person.name).toStrictEqual(new Name("Saravanan", "Lakshamanan"));
  • expect(person.born.bornAt).toStrictEqual(new Address(100, "Hospital street", "Tamil Nadu", "India"));
  • expect(person.address.street).toStrictEqual("Coder Street");
2

I may just not be understanding the exercise, but get(person) and set(person, value) are defined in the Lens class, but they aren’t necessary since the values provided when using the class replace them.

Also I think there should be more tests, to discourage hard-coding.

Opinion

Also I don’t think the premise of this exercise is entirely valid?
The example given from Haskell does indeed seem very messy, but it isn’t nearly as bad in JavaScript.
Plus why is there a need for an exercise about this functional programming concept in (what I believe to be) an object-oriented language?

3

We can think about functional programming as being a mindset. Some programming languages have many features that specifically support it.

I would suggest that the React framework is built with a functional mindset.

4

@FriendlyUser1 In my humble opinion Javascript, as it is used today in most environments, is very much a functional language. Yes, it supports OOP functionality but with most modern frameworks it feels like that’s really not the focus. It’s very much a matter of choice tho.

AS for the exercise tests, PRs are welcome if you have the time and energy to work on this. You’d also want to discuss with @SleeplessByte (our resident JS track maintainer (sorry for the ping)).

1 Like
5

Adding tests to ensure the immutability (and fixing the typos) is accepted and we’ll take a PR.

6

Opened a PR

7

Merged! You should see the change on the website shortly.

1 Like