Update `grade-school` tests

[Elahi-cs]

This PR aims to update all tests in the grade-school exercise. The tests were created manually because the fact that some object-oriented adjustments were necessary made it impossible for the exercise_creation_helper to actually help. I'm hesitant the changes were done correctly because of my lack of experience with the platform, but I've tried to stick to the original test cases where possible and to use the same style with the missing test cases.

@vaeng let me know what you think.

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[vaeng]

Thanks for the update. Something broke, so the tests are not passing

[Elahi-cs]

Thanks for the update. Something broke, so the tests are not passing

@vaeng I might need a little bit of guidance on this one. After running configlet, several new tests were added that were not there before. I've done my best to implement them, but some of them are not passing the pipeline tests. An example of this is Cannot add student to same grade in the roster more than once. This was my implementation:

TEST_CASE("Cannot add student to same grade in the roster more than once",
          "[87c871c1-6bde-4413-9c44-73d59a259d83]") {
    grade_school::school school_;
    school_.add("Blair", 2);
    school_.add("James", 2);
    school_.add("James", 2);
    school_.add("Paul", 2);
    REQUIRE(school_.grade(2) == vector<string>{"Blair", "James", "Paul"});
}

However it doesn't seem to be required by the solutions:

/home/runner/work/cpp/cpp/build_exercises/practice/grade-school/grade_school_test.cpp:59: FAILED:
  REQUIRE( school_.grade(2) == vector<string>{"Blair", "James", "Paul"} )
with expansion:
  { "Blair", "James", "James", "Paul" }
  ==
  { "Blair", "James", "Paul" }

Should I disregard these tests and mark them as not included in the tests.toml? Or is there something wrong with either my implementation or the pipeline checks?

Thanks in advance.