[BUG] Empty string is not a valid UINT32
[TASK] Refactor trustline test code to reduce duplication and test response body before status code and headers

[TASK] Use object for arguments to checkGetRequest and checkPostRequest

[TASK] Clean up trustline test code, change parameter names, function signatures

[TASK] Make arguments to testGetRequest and testPostRequest mandatory
Merge pull request #231 from lumberj/bug/empty_string_not_uint32

[BUG] Empty string is not a valid UINT32
Merge pull request #226 from clark800/feature/trustline_tests_refactor

[TASK] Refactor trustline test code