Add unit tests for get_objects_in_term()

[rodrigosprimo]

The attached patch adds three basic unit tests for get_objects_in_term()

[johnbillion]

Thanks!

Only thing I would change is to switch to using $terms->get_error_code() or $terms->get_error_message() in test_get_objects_in_term_should_return_invalid_taxonomy_error(), instead of using $terms->errors['invalid_taxonomy'][0] directly.

[rodrigosprimo]

Patch updated to use $terms->get_error_message(). Thanks for your feedback.

[jorbin]

In 33182:

Add Unit Tests for get_objects_in_term()

Props rodrigosprimo.
Fixes #32946.