689: translations not generated for choice list used with search() [tests]

[lindsay-stevens]

Follow up to #690 to finish the test cases.

Why is this the best possible solution? Were any other approaches considered?

Covers use cases in relation to choice / translation behaviour per the XLSForm docs. I found the numbered list there a bit abstract, so for reference this docs page from SurveyCTO has good illustrations of the advanced usages.

What are the regression risks?

None, it's just tests.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

Not directly, but I noticed a dead link on the XLSForms docs page. Not sure if the file is gone or it's a permissions issue:

For an example, see the advanced search-and-select sample form here.

Before submitting this PR, please make sure you have:

• [x] included test cases for core behavior and edge cases in tests
• [x] run nosetests and verified all tests pass
• [x] run black pyxform tests to format code
• [x] verified that any code or assets from external sources are properly credited in comments