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Problem Specifications

Shared metadata for Exercism exercises.

Reviewing Guidelines

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  • If you think that a PR should not be merged, either as is or in general, please leave a review requesting changes.
  • Please also use the Request Changes button if you are unsure about how a concern of yours could be resolved.
    • This will block the PR from being merged until the change request has been addressed / overruled by an admin.
    • It ensures that your thoughts will be heard and can be addressed rather than being overruled by a majority.
  • When a discussion goes stale or there are several opposing views and a compromise cannot be reached, ping @exercism/maintainers-admin to resolve the discussion.

Exercise Metadata

Each exercise's metadata lives in a directory under exercises/.

exercises/
 accumulate
  description.md
  metadata.toml
 ...
 minesweeper
  canonical-data.json
  description.md
  metadata.toml
 ...
 zipper
     description.md
     metadata.toml

There are three metadata files per exercise:

  • description.md - the basic problem description
  • metadata.toml - additional information about the exercise, such as where it came from
  • canonical-data.json (optional) - standardized test inputs and outputs that can be used to implement the exercise

Test Data (canonical-data.json)

Test data can be incorporated into a track's test suites manually or extracted by a program (a.k.a. a test generator).

  • Exercises must contain tests that cover the public interface of the exercise (also thought of as "application tests").

  • Exercises may contain tests that cover the private or lower-level interface of the exercise (sometimes referred to as "library tests").

  • Test cases are immutable, which means that once a test case has been added, it never changes. There are two exceptions:

    • The comments field can be mutated and thus does not require adding a new test case when changing its value.
    • The description field can be mutated and thus does not require adding a new test case when changing its value.
    • The scenarios field can be mutated additively, by adding new scenarios. Existing scenarios must not be changed or removed. Adding new scenarios thus does not require adding a new test case.
  • Test cases must all be considered optional, insomuch that a track should determine per test case whether to implement it or not.

  • Each test case has a UUID (v4) to uniquely identify it.

  • If tracks automatically generate test suites from test data, they must do that based on an explicit list of test cases to include/exclude. Test cases must be identified by their UUID, and we'll provide tooling to help keep track of which test cases to include/exclude.

Test Data Format

The file format is described in canonical-data.schema.json, but it is easier to understand with an example:

{
  "exercise": "foobar",
  "comments": [
    " Comments are always optional and can be used almost anywhere.      ",
    "                                                                    ",
    " They usually document how the exercise's readme ('description.md') ",
    " is generally interpreted in test programs across different         ",
    " languages.                                                         ",
    "                                                                    ",
    " In addition to a mainstream implementation path, this information  ",
    " can also document significant variations.                          "
  ],
  "cases": [
    {
      "comments": [
        " A test case must have 'uuid', 'description', 'property', ",
        " 'input' and 'expected' properties. The rest is optional. ",
        "                                                          ",
        " The 'property' is a string in lowerCamelCase identifying ",
        " the type of test, but most of the times it is just the   ",
        " name of a function being tested.                         ",
        "                                                          ",
        " Test cases can have any number of additional keys, and   ",
        " most of them also have an 'expected' one, defining the   ",
        " value a test should return.                              "
      ],
      "uuid": "31e9db74-86b9-4b14-a320-9ea910337289",
      "description": "Foo'ing a word returns it reversed",
      "property": "foo",
      "input": {
        "word": "lion"
      },
      "expected": "noil"
    },
    {
      "uuid": "09113ce5-b008-45d0-98af-c0378b64966b",
      "description": "Bar'ing a name returns its parts combined",
      "property": "bar",
      "input": {
        "firstName": "Alan",
        "lastName": "Smithee"
      },
      "expected": "ASlmainthee"
    },
    {
      "comments": [
        " Test cases can be arbitrarily grouped with a description ",
        " to make organization easier.                             "
      ],
      "description": "Abnormal inputs: numbers",
      "cases": [
        {
          "uuid": "f22d7a03-e752-4f14-9231-4eae9f128cef",
          "description": "Foo'ing a number returns nothing",
          "property": "foo",
          "input": {
            "word": "42"
          },
          "expected": null
        },
        {
          "uuid": "8790a635-e8a8-4343-a29f-7da2929b9378",
          "description": "Foo'ing a very big number returns nothing",
          "comments": ["Making this test case pass requires using BigInts."],
          "scenarios": ["big-integers"],
          "property": "foo",
          "input": {
            "word": "28948022309329048855892746252171976962977213799489202546401021394546514198529"
          },
          "expected": null
        },
        {
          "uuid": "c7b6f24a-553f-475a-8a40-dba854fe1bff",
          "description": "Bar'ing a name with numbers gives an error",
          "property": "bar",
          "input": {
            "firstName": "HAL",
            "lastName": "9000"
          },
          "expected": {
            "error": "You should never bar a number"
          }
        }
      ]
    }
  ]
}

Scenarios

An optional field to allow for selectively including/excluding test cases based on a property of the test case (such as using big integers).

  • The scenarios field can use one or more of a predefined set of values, which are defined in a SCENARIOS.txt file.
  • The scenarios field can be mutated additively, by adding new scenarios. Existing scenarios must not be changed or removed. Adding new scenarios does therefore does not mean adding a new test case.
  • Library tests should have a library-test scenario added to allow for easy including/excluding of library tests. Application tests won't have their own scenario, as they must be included and should not be filtered on.

Changing Tests

As test cases are immutable, a "bug fix" requires adding a new test case. We'll add metadata to test cases to link a re-implementation of a test case to the re-implemented test case.

  • Re-implemented test cases must have a reimplements field which contains the UUID of the test case that was re-implemented.
  • Re-implemented test cases must use the comments field to explain why a test case was re-implemented (e.g. "Expected value is changed to 2").
  • Track generators should not automatically select the "latest" version of a test case by looking at the "reimplements" hierarchy. We recommend each track to make this a manual action, as the re-implemented test case might actually make less sense for a track.

This is an example of what a re-implementation looks like:

[
  {
    "uuid": "e46c542b-31fc-4506-bcae-6b62b3268537",
    "description": "two times one is two",
    "property": "twice",
    "input": {
      "number": 1
    },
    "expected": 3
  },
  {
    "uuid": "82d32c2e-07b5-42d9-9b1c-19af72bae860",
    "reimplements": "e46c542b-31fc-4506-bcae-6b62b3268537",
    "description": "two times one is two",
    "comments": ["Expected value is changed to 2"],
    "property": "twice",
    "input": {
      "number": 1
    },
    "expected": 2
  }
]

Track Data

Exercism deliberately requires that every exercise has its own copy of certain files (like .docs/instructions.md). There is a tool called configlet, which can check that Practice Exercises on a track are in sync with the problem-specifications source, and can update them when updates are available.

Track Test Data

If a track implements an exercise for which test data exists, the exercise must contain a .meta/tests.toml file. The goal of this file is to keep track of which tests are implemented by the exercise. Tests in this file are identified by their UUID and each test has a boolean value that indicates if it is implemented by that exercise.

A tests.toml file for a track's two-fer exercise might contain:

[19709124-b82e-4e86-a722-9e5c5ebf3952]
description = "no name given"

[3451eebd-123f-4256-b667-7b109affce32]
description = "a name given"
include = false

[653611c6-be9f-4935-ab42-978e25fe9a10]
description = "another name given"
comment = "comments like this will persist across syncs"

In this case, the track has chosen to implement two of the three available tests (include = true is the default and is omitted).

If a track uses a test generator to generate an exercise's test suite, it must use the contents of the tests.toml file to determine which tests to include in the generated test suite.

Track Data Tooling

To make it easy to keep the data in the track exercises up to date, the configlet application provides a sync command. There are three kinds of data that can be updated from problem-specifications: documentation, metadata, and tests.

A plain configlet sync makes no changes to the track, and checks every data kind for every exercise. For example, it compares the tests specified in the tests.toml files against the tests that are defined in the exercise's canonical data - if there are tests defined only in the latter, it prints a summary and exits with a non-zero exit code.

To interactively update the instructions.md, tests.toml and metadata files, use configlet sync --update.

For documentation and metadata, this prompts the user whether to sync the data with the latest version in problem-specifications. For each missing test, there is a prompt to choose whether to include/exclude/skip it. Configlet then updates the corresponding tests.toml file accordingly.

To non-interactively include every missing test for an exercise foo, use:

configlet sync --tests include --exercise foo --update

or the short form configlet sync --tests include -e foo -u.

Refer to the documentation for configlet sync for more details on the various command options.

The sync command operates on Practice Exercises that are in the track-level config.json file. If you are adding an exercise that has canonical data to a track, first add that exercise to the track-level config.json, and then run a configlet sync command to create the corresponding tests.toml file.

To download the latest version of the configlet tool, please run the fetch-configlet bash script or the fetch-configlet.ps1 PowerShell script (Windows only). At least one of these scripts should already exist in every track repo's bin directory - the script will also download configlet to this location. You can then sync the tests by running ./bin/configlet sync (on macOS/Linux/similar) or .\bin\configlet.exe sync (on Windows).

Conventions

There are also some conventions that must be followed:

  • Descriptions should not simply explain what each case is (that is redundant information) but also why each case is there. For example, what kinds of implementation mistakes might this case help us find?
  • All keys should follow the lowerCamelCase convention.
  • If the input is valid but there is no result for the input, the value at "expected" should be null.
  • If an error is expected (because the input is invalid, or any other reason), the value at "expected" should be an object containing exactly one property, "error", whose value is a string.
    • The string should explain why the error would occur.
    • A particular track's implementation of the exercise need not necessarily check that the error includes that exact string as the cause, depending on what is idiomatic in the language (it may not be idiomatic to check strings for error messages).

Validation

canonical.json files can be validated against its schema using https://www.jsonschemavalidator.net/ with...

{
  "$schema": "https://github.com/exercism/problem-specifications/blob/main/canonical-data.schema.json"
}

New Exercises Require a Glyph

When creating a new exercise the design team needs to be informed so that a new glyph can be created.

  • An issue should be opened in exercism/website-icons after a PR has been opened in problem-specifications.
  • This issue should reference the PR in problem-specifications.

Automated Tests

canonical-data.json for each exercise is checked for compliance against the canonical-data.schema.json. In order to run these tests, you will need to have yarn installed on your system. Install them from here.

Install the required packages:

yarn install

Run for all exercises:

yarn test

Run for single exercise:

yarn run test-one exercises/<exercise>/canonical-data.json

Replace <exercise> by the name of exercise which you want to check.

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