Improve test suite

[clue]

The test suite currently only consists of functional tests which send actual SOAP requests against a public SOAP API.

This means that our test suite is useless if this webservice should (ever) be down.

We should look into adding proper unit tests and perhaps another functional test case.

[clue]

FWIW: Another possible functional webservice: http://api.bioinfo.no/wsdl/EchoService.wsdl

[clue]

For the reference: #11 is now in, this should probably help with mocking from a local WSDL file.