Throw 500 and 501 errors for missing or invalid handlers in SCIMMY.Resources.User and SCIMMY.Resources.Group

[sleelin]

Currently, the read, write, and patch methods of the SCIMMY.Resources.User and SCIMMY.Resources.Group classes pass return values from declared ingress/egress/degress handlers directly to their corresponding schema classes for instantiation. When these handlers are either missing, or do not return expected values, the schema class constructor will throw a TypeError exception, as it expects the supplied value to be an object. This TypeError exception is then rethrown as a SCIMError exception with status and scimType properties of values 400 and invalidValue respectively, indicating an issue with the request, which is technically incorrect.

This change updates the default ingress, egress, and degress handlers for the User and Group resource classes to throw a 501 Not Implemented exception (fixes #39). It also updates the the read and write methods of these classes to throw a 500 Internal Server Error when handler implementations return invalid or empty values that cannot be coerced into schema-compliant values (fixes #39). Additionally, the patch method of these classes have been updated to call the class read and write methods to leverage the aforementioned exception handling, instead of calling ingress/egress handlers themselves (fixes #39). The patch methods have also been updated to require they are only able to be called for a specific resource, instead of for a list of resources. The test fixtures in the resources hooks have been updated to verify the correct exceptions are being thrown, and that the patch method now requires a specific resource.