Add more v2, v3, and v4 task metadata tests

[amogh09]

Summary

• Add more tests for v2, v3, and v4 task metadata endpoints. Currently there are some error cases that are not covered by existing tests. This change fills that gap in coverage.
• General improvements to the test file.
  • Replace some global variables for expected responses with getter functions so that tests are free to mutate the expected responses if needed without affecting other tests.
  • Consolidate all cases for v2, v3, and v4 task metadata endpoints into one test each to promote code reuse and improve readability and maintainability.

Implementation details

• Add TestV2TaskMetadata, TestV3TaskMetadata, and TestV4TaskMetadata functions for testing v2, v3, and v4 task metadata endpoints, respectively. These test functions include all happy and error cases. Remove existing tests for these endpoints as they are covered in the new test functions.
• Replace some global variables with getter functions for better test isolation (tests are free to mutate the values returned by the getter functions without affecting other tests).

Testing

New tests cover the changes: yes

Description for the changelog

Add more v2, v3, and v4 task metadata tests

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.