The following endpoints are missing:

• operations: update-to-one-relationship
• operations: update-to-many-relationship
• operations: add-to-relationship
• operations: delete-from-relationship

Relationships come in two flavors: to-one (data contains an object in the request body) and to-many (data contains an array in the request body). We should have coverage for both.

Additionally, data can contain either a resource object (consisting of attributes and/or relationships), or a resource identifier object (consisting of types/ids, but no fields). See the JSON:API spec for details and examples.

Furthermore, there are additional places where meta can occur in request bodies. For example:

var document = new Document
{
 Meta = [],
 Data = new SingleOrManyData<ResourceObject>(new ResourceObject
 {
 Meta = [],
 Relationships = new Dictionary<string, RelationshipObject?>
 {
 ["some"] = new()
 {
 Meta = [],
 Data = new SingleOrManyData<ResourceIdentifierObject>(new ResourceIdentifierObject
 {
 Meta = []
 })
 }
 }
 }),
 Operations =
 [
 new AtomicOperationObject
 {
 Meta = [],
 Data = new SingleOrManyData<ResourceObject>(new List<ResourceObject>
 {
 new()
 {
 Meta = [],
 Relationships = new Dictionary<string, RelationshipObject?>
 {
 ["some"] = new()
 {
 Meta = [],
 Data = new SingleOrManyData<ResourceIdentifierObject>(new List<ResourceIdentifierObject>
 {
 new()
 {
 Meta = []
 }
 })
 }
 }
 }
 })
 }
 ]
};

For demonstration, I've used data arrays only in operations above, but single/many can occur in all places.

Based on all the possible combinations, I don't think it makes sense to separate tests by the place where meta occurs (top-level, data, relationship, etc.). It would be easier to have a single test per endpoint/operation that contains all possible locations for that endpoint. However, because we're dealing with both to-one and to-many relationships, we'll need separate endpoints (because SupportTicket contains a to-one, whereas ProductFamily contains a to-many).

So, for example:

• Accepts_meta_in_patch_resource_request_with_to_one_relationship: PATCH /supportTickets
• Accepts_meta_in_patch_resource_request_with_to_many_relationship: PATCH /productFamilies

Oh, and relationship endpoints don't take attributes/relationships, so they should be removed from the existing tests.

This is not a post-relationship request. It is a post-resource request that includes a relationship.
A post-relationship request would look like:

POST /supportTickets/1/relationships/productFamily
{
 "data": {
 "type": "productFamilies",
 "id": "5"
 }
}