Add CONTRIBUTING guide for constraints portion of codebase

src/validations/constraints/CONTRIBUTING.md

@@ -0,0 +1,161 @@
+# Contributing to constraints and tests
+
+This document guides developers through changing or extending code and data in in this folder and sub-folders. They contain the constraints to check FedRAMP requirements for OSCAL data and a test harness. The test harness includes unit tests, valid, and invalid OSCAL fixture data for those tests.
+Before contributing to this portion of the codebase, please review the and follow the guidance in the [project contribution page](../../../CONTRIBUTING.md).
+## Overview of the constraint and testing infrastructure
+
+The diagram below highlights how different constraints, tests, fixture data with invalid and valid OSCAL documents, and dependencies function together.
+
+```mermaid
+flowchart TD
+    BuildTool[make build-validations] -->|runs| NpmRunner[npm test]
+    NpmRunner -->|runs| TestRunner[cucumber]
+    TestRunner -->|loads test descriptions from| TestRunnerExtension(fedramp_extension.feature)
+    TestRunnerExtension[fedramp_extension.feature] -->|using the helper| TestRunnerImplementation(fedramp_extension_steps.ts)
+    TestRunnerImplementation -->|imports| CLIWrapper(oscal-js)
+    TestRunnerImplementation-->|loads| TestConfiguration(YAML test inventory)
+    TestRunnerImplementation-->|exports unit test results| UnitTestResults(reports/constraints.html)
+    CLIWrapper -->|configures and runs| CLI(oscal-cli)
+    CLI-->|loads| ConstraintFile(constraint XML files)
+    CLI -->|validates| TestFixtures(OSCAL test content)
+    CLI -->|return| CLIResult(exit code and SARIF results)
+    CLIResult -->|interpreted by| CLIWrapper
+    CLIWrapper -->|SARIF in memory| TestRunnerImplementation
+```
+
+## How do I install tools for development and testing?
+
+After you [install the prerequisites](./README.md#31-prerequisites), you can use `make` to properly configure tools and their dependencies.
+
+```sh
+cd path/to/fedramp-automation
+make init
+```
+
+## How do I run the tests?
+
+To run the existing tests as-is, you can use `make` or `npm` directly.
+
+```sh
+cd path/to/fedramp-automation
+# use make
+make test
+# or use npm from the top-level directory
+npm test
+# or use it from within this directory
+cd src/validations/constraints
+npm test
+```
+
+## How do I run the tests for a specific constraint?
+
+To run tests for a specific constraint or a selection of several constraints, you can use `npm run` as follows.
+
+```sh
+cd path/to/fedramp-automation
+# to test a constraint with the ID <my-constraint-id>
+npm run constraint <my-constraint-id>
+
+# to get a list of one or more constraints to select for testing
+npm run constraint 
+## How do I add a constraint and test?
+
+You can add a constraint and test to this repository by following these high-level steps.
+
+1. Create a new constraint in [the appropriate constraints file](#which-constraint-file-do-i-edit). Note the `id`, you will use it later.
+2. Add the necessary, correct data to [`./content/ssp-all-VALID.xml`](./content/ssp-all-VALID.xml) for a positive test of the constraint.
+3. Add the YAML metadata for the positive test in [`./unit-tests`](./unit-tests/). The name of the file should start with the name of the assembly, field, or flag, and end with `-PASS.yaml`. For example, a new constraint and test for a [`//metadata/party/prop`](https://pages.nist.gov/OSCAL-Reference/models/v1.1.2/system-security-plan/json-reference/#/system-security-plan/metadata/parties) assembly should be `party-PASS.yaml`. The content should be like the example below.
+
+```yaml
+# ./unit-tests/party-PASS.yaml
+test-case:
+  name: Positive Test for party
+  description: This test case validates the behavior of constraint party
+  content: ../content/ssp-all-VALID.xml
+  expectations:
+    - constraint-id: party
+      result: pass
+```
+
+4. Add the necessary, incorrect data to [`./content/ssp-all-INVALID.xml`](./content/ssp-all-INVALID.xml) for a positive test of the constraint.
+5. Add the YAML metadata for the negative test in [`./unit-tests`](./unit-tests/). The name of the file should start with the name of the assembly, field, or flag, and end with `-FAIL.yaml`. For example, a new constraint and test for a `//metadata/party/prop` assembly should be `party-FAIL.yaml`. The content should be like the example below.
+
+```yaml
+# ./unit-tests/party-FAIL.yaml
+test-case:
+  name: Negative Test for party
+  description: This test case validates the behavior of constraint party
+  content: ../content/ssp-all-INVALID.xml
+  expectations:
+    - constraint-id: party
+      result: fail
+```
+
+6. Update the test descriptions in [Cucumber feature file](https://cucumber.io/docs/gherkin/reference/), [`../../../features/fedramp_extensions.feature`](../../../features/fedramp_extensions.feature). Add the file names between `#BEGIN_DYNAMIC_TEST_CASES` and `#END_DYNAMIC_TEST_CASES` blocks in alphabetical order so the test runner discovers them. Add the constraint ID between the `#BEGIN_DYNAMIC_CONSTRAINT_IDS` and `#END_DYNAMIC_CONSTRAINT_IDS` in alphabetical order so the test runner can perform code coverage analysis. The updated content should like the example below.
+
+```yaml
+# Beginning of file truncated
+#BEGIN_DYNAMIC_TEST_CASES
+# There will be existing test case files, you are adding these below
+  | party-FAIL.yaml |
+  | party-PASS.yaml |
+#END_DYNAMIC_TEST_CASES
+# Middle of file truncated
+#BEGIN_DYNAMIC_CONSTRAINT_IDS
+# There will be existing constraint IDs, you are adding this one below
+  | party |
+#END_DYNAMIC_CONSTRAINT_IDS
+# End of file truncated
+```
+
+7. You can now [run the test harness](#how-do-i-run-the-tests) and confirm the new tests are correct.
+8. Update the files with [`git add`](https://git-scm.com/docs/git-add) and [`git commit`](https://git-scm.com/docs/git-commit) to a branch for a pull request [that follows our guidance](../../../CONTRIBUTING.md#contributing-to-this-github-repository).
+
+## How do I modify a test?
+
+To modify a test, you may possibly need to change the constraint, valid test data, invalid test data, the test case YAML file(s), and the Cucumber inventory.
+
+To change the test data for a test developers [previously added with the correct steps](#how-do-i-add-a-constraint-and-test), you only need to modify the valid or invalid data in [`./content`](./content).
+
+To change the `test` or `target` of a constraint developers [previously added with the correct steps](#how-do-i-add-a-constraint-and-test), you may only need to adjust the constraint [in the appropriate constraint file](#which-constraint-file-do-i-edit), the valid data, and/or invalid data, but not other files. What and why you will change determines if some or all those files need a modification.
+
+To change the `id` of a constraint developers [previously added with the correct steps](#how-do-i-add-a-constraint-and-test), you must make more changes.
+
+1. You must update the `id` [in the appropriate constraint file](#which-constraint-file-do-i-edit).
+1. You must use [`git mv`](https://git-scm.com/docs/git-mv) to rename the test case files in [`./unit-tests`](./unit-tests) with relevant changes to the assembly, field, or flag and ID.
+1. You must update the files names and constraint ID in [`../../../features/fedramp_extensions.feature`](../../../features/fedramp_extensions.feature) accordingly.
+1. Update the files with [`git add`](https://git-scm.com/docs/git-add) and [`git commit`](https://git-scm.com/docs/git-commit) to a branch for a pull request [that follows our guidance](../../../CONTRIBUTING.md#contributing-to-this-github-repository)..
+
+## How do I delete a constraint and test?
+
+1. You must use [`git rm`](https://git-scm.com/docs/git-rm) to delete the relevant test case files in [`./unit-tests`](./unit-tests).
+1. You must remove the relevant files names and constraints by their ID in [`../../../features/fedramp_extensions.feature`](../../../features/fedramp_extensions.feature) accordingly. Use [`git add`](https://git-scm.com/docs/git-add) with this file to record the deleted lines of the file.
+1. You must remove the constraints by their ID in one or more of the relevant [constraint files](#which-constraint-file-do-i-edit) and use [`git add`](https://git-scm.com/docs/git-add) to record the deleted lines of the file.
+1. Update the files with [`git commit`](https://git-scm.com/docs/git-commit) to a branch for a pull request [that follows our guidance](../../../CONTRIBUTING.md#contributing-to-this-github-repository).
+
+## Which constraint file do I edit?
+
+### `fedramp-external-allowed-values.xml`
+
+The [`fedramp-external-allowed-values.xml`](./fedramp-external-allowed-values.xml) file contains [Metaschema constraints](#how-do-i-learn-more-about-metaschema-and-metapath) specific to FedRAMP use cases and requirements for data in the OSCAL information model. Specifically, developers only maintain constraints in this file if they are simple [`allowed-values` checks](https://pages.nist.gov/metaschema/specification/syntax/constraints/#allowed-values-constraints). FedRAMP developers maintain constraints of all types in the [`fedramp-external-constraints.xml`](#fedramp-external-constraintsxml) file.
+
+### `fedramp-external-constraints.xml`
+
+The [`fedramp-external-constraints.xml`](./fedramp-external-constraints.xml) file contains [Metaschema constraints](#how-do-i-learn-more-about-metaschema-and-metapath) specific to FedRAMP use cases and requirements for data in the OSCAL information model. Specifically, developers maintain all constraints in this file that are *not* simple [`allowed-values` checks](https://pages.nist.gov/metaschema/specification/syntax/constraints/#allowed-values-constraints).
+
+### `oscal-external-constraints.xml`
+
+The [`oscal-external-constraints.xml`](./oscal-external-constraints.xml) file contains [Metaschema constraints](#how-do-i-learn-more-about-metaschema-and-metapath) that can complement the existing constraints [embedded directly into the official upstream NIST OSCAL models](https://github.com/usnistgov/OSCAL/tree/v1.1.2/src/metaschema). The proposed constraints in this file support improved long-term maintenance and extensibility with the intent to merge upstream. Therefore, FedRAMP developers do *not* use this file for any constraint specific to FedRAMP use cases or requirements in the OSCAL information model.
+
+**NOTE**: The FedRAMP Automation Team will make a best effort attempt to collaborate with NIST maintainers to merge them upstream and deprecate from this repository accordingly. Until further notice, the FedRAMP Automation Team maintains them here for testing and evaluation until they are sufficiently mature to contribute them upstream.
+
+## How do I learn more about Metaschema and Metapath?
+
+To add or modify constraints and their tests, it is important to understand Metaschema syntax, particularly constraint syntax and Metapath syntax for `@test` and `@target` in the constraints. You can review these pages for more information.
+
+- [Metaschema constraint syntax](https://pages.nist.gov/metaschema/specification/syntax/constraints/)
+- [Metapath expression language](https://pages.nist.gov/metaschema/specification/syntax/metapath/)
+- [Metaschema tutorials for modeling and constraints](https://pages.nist.gov/metaschema/tutorials/)
+- [Metaschema complete syntax reference](https://pages.nist.gov/metaschema/specification/syntax/)
+
+## How do