rest api: missing unit tests package

[rudolfix]

following unit test that check processing of RESTAPIConfig and resource generation

incremental

• [x] test if Incremental is properly instantiated from IncrementalArgs. This is a unit test for function setup_incremental_object and we test that (Incremental, IncrementalParam) are properly constructed from the config dict.
• [x] test if incremental is properly bound to start_param and end_param (IncrementalConfig). Similar to before, just the second branch of the function.
• [x] test many incrementals in single resource. This should fail.
• [x] incremental bound via parameter. (probably line 166)
• [x] incremental bound via dlt.sources.incremental (probably line 164)

resource generation

• [x] check if resource receives all resource hints possible (table_name, parallel, max nesting etc.)

transformers (child resource) generation (declarative interface)

• [x] binding to non existing resource
• [x] two dependent resources to one resource
• [x] one dependent resources binding two resources (should fail)
• [x] I assume we do not support resource -> transformer -> transformer but also this must be tested,. Answer: we do support that!
• [x] circular dependencies. Should fail with CycleError, probably already raised by topological_sort().
• [x] test include fields from parent, also non existing fields

test binding of params

• [x] path params vs query params vs body params (what if path param is not bound) (path and query params are tested)