grade-school test for student in multiple grades does not make sense

[wolf99]

problem-specifications/exercises/grade-school/canonical-data.json

Line 19 in eb6c32b

"description": "A student can't be in two different grades",

Firstly this test has desiredGrade as an input, but is a test of the roster property, this input is otherwise only used with the grade property. This does not make sense in terms of the functionality required for the properties

students_t roster(input); // this case, and only this case, implies adding desired_grade argument here also, which does not make sense
students_t grade(input, desired_grade);

This seems like possibly just a mistake of copy-pasta roster when grade was intended. Thus the solution would be simply to change the property under test from roster to grade. I can add a PR to resolve this if I have understood correctly?

A second issue is that the students input is intended, per the README.md, one by one. This implies some order of addition. The order used does not matter, just that there must be one.
However, the desiredGrade is then queried later.
So a function used to add students (e.g. add_student(student_t student) ) could check inputs for duplicate names, but it can only prevent second and third additions. It cannot know in advance of adding the first name that a second name will be added that will conflict with it.

Thus the input of the following cannot make sense given that the desiredGrade, that should return an empty roster, is the first student to be added:

            "students": [
              ["Aimee", 2],
              ["Aimee", 1]
            ],
            "desiredGrade": 2

If instead, we say that addition of students should not be filtered, but instead the grade() function should filter what gets output from the data that has been added; then yes, this can work, but it is ugly and requires poor implementation in just about any language I know (true, I don't know a lot of languages 😄 ).

A solution to this problem can be that the README.md is added to remove suggestions about what implementation should be - just describe the problem and let languages implement a solution in an idiomatic manner. Is this correct understanding, maybe I have missed something?

[SleeplessByte]

The property should probably be neither grade nor roster, but a new property that's basically: student is only in grade n, where n = 2.

I don't really understand the rest of the issue (I mean the second point). The end goals is that Aimee can only be added once. The person who came up with the test wanted the "first one" to win. Does that help?

[petertseng]

Oh ha... missed this when updating my verifier for that new case... my verifier simply ignores the desiredGrade property and thereby passes all tests by declaring that a students that's added twice is in none of the grades... that's a mistake on my part. I'll update the verifier write some thing to show me cases with inconsistent input keys per property.

[ErikSchierboom]

The property should probably be neither grade nor roster, but a new property that's basically: student is only in grade n, where n = 2.

To me it sounds like this is an error case, in which case using the existing grade or roster property is fine, but we should remove the desiredGrade property and convert the expected value to an error case.

[wolf99]

In terms of trying to build a JSON that makes sense, either of the following seems more logical than current spec:

        {
          "uuid": "dece43c8-3ba5-11eb-8fdf-7f8daeaeb5f2",
          "description": "A student can't be in two different grades",
          "property": "roster",
          "input": {
            "students": [
              ["Aimee", 2],
              ["Aimee", 1]
            ]
          },
          "expected": [ "Aimee" ]
        },

        {
          "uuid": "dece43c8-3ba5-11eb-8fdf-7f8daeaeb5f2",
          "description": "A student can't be in two different grades",
          "property": "grade",
          "input": {
            "students": [
              ["Aimee", 2],
              ["Aimee", 1]
            ],
            "desiredGrade": 1
          },
          "expected": []
        },

But it shouldn't be the mix of both that it seems to be currently.

Ideally... the JSON should spec and test some sort of addStudent functionality, as that functionality is what is outlined in the description.md - then that should result in an error when trying to add Aimee for a second time.

[wolf99]

OK, here's my logic using examples from the existing description.md.

If, as @SleeplessByte has mentioned, the first addition of a student "wins", then Aimee is added to the roster in grade 2

Taking a literal transposition of the rules in the description.md:

• Get a sorted list of all students in all grades. Grades should sort
  as 1, 2, 3, etc., and students within a grade should be sorted
  alphabetically by name.
  • "Who all is enrolled in school right now?" (== property: roster)
  • --- "Oh and just this time especially, lets throw a grade = 2 requirement in the mix, i.e. forget what I just said in the first step about all grades." (== desiredGrade: 2)
  • "Let me think. We have"
    "No-one" (This does not make any sense at all to me, Aimee is definitely in at least one of the grades!)

This is the only test case that uses the desiredGrade input with the roster property which, as you can see from the example, it does not make sense to do. And the result does not indicate anything about the grade of Aimee.

Thus there are two other ways of interpreting this, firstly, keep the property as roster, and remove the desiredGrade.
I think this option makes more logical sense than the current test case, but still does not tell us anything about Aimee's grade.

• Get a sorted list of all students in all grades. Grades should sort
  as 1, 2, 3, etc., and students within a grade should be sorted
  alphabetically by name.
  • "Who all is enrolled in school right now?" (== property: roster)
  • "Let me think. We have"
    "Anna"

Alternatively, change the property to grade and the desiredGrade to 1:

• Get a list of all students enrolled in a grade
  • "Which students are in grade 1?" (== property: grade, desiredGrade: 1)
  • "No-one"

This last option makes logical sense and the output tells us that Aimee is not in grade 1 as the input may otherwise imply.