Implement initial coverage for REGAPIC via Gapic-Showcase. We want to try and reach some parity with the tests that are implemented in Golang, but we may not strive to implement everything done in Golang and may not copy their structure.

Plans for implementation:

• Callables (Echo)
  • Unary - PR at chore: Add Showcase Callables IT #1483
  • Server Side Streaming - PR at chore: Add httpjson server-side streaming showcase tests #1588
• Behaviors (Echo)
  • Deadline - PR at fix: Unary Callables Deadline values respect the TotalTimeout in RetrySettings #1603
  • Pagination - PR at chore: Add pagination showcase tests #1635
  • Retry - PR at fix: Unary Callables Deadline values respect the TotalTimeout in RetrySettings #1603
• Http Annotation - query/ path/ body combinations (Compliance) - PR: chore: Add Showcase Http Annotations Test #1568
• CRUD (Identity) - PR: chore: Add HttpJson CRUD Showcase tests #1589
  • Get
  • List
  • Create
  • Delete
  • Update
• Mixins (Echo)
  • Location - PR: chore: Add HttpJson Showcase test for Location Mixins #1656
  • IAM - PR: chore: Implement gRPC and HttpJson showcase tests for IAM #1789
  • Operations - PR at fix: Unary Callables Deadline values respect the TotalTimeout in RetrySettings #1603

Bugs/ Blockers:

• https://github.com/googleapis/gapic-generator-java/issues/1440 (Part 1 completed, Part 2 is not required)
• Set the default charset as UTF-8 for REST calls with application/json MediaType #1437
• HttpJson Unary Callables not following RetrySetting's TotalTimeout value #1504
• HttpJson UpdateUserRequest's FieldMask is unable to be Unmarshalled gapic-showcase#1263
• Allow HTTP POST calls for any showcase PATCH RPCs gapic-showcase#1261
• com.google.showcase.v1beta1.MessagingClientHttpJsonTest#updateBlurbTest failing with 404 error #1547
• HttpJson ServerSideStreaming error in EchoClient gapic-showcase#1286
• HttpJson Mixins RPCs (Locations & IAM) Not Supported gapic-showcase#1299
• IAM Policy Mixin for HttpJson matches incorrect Mux Handler gapic-showcase#1338