test coverage

[ghost]

There are no tests for the topology module. Tests could be derived from the examples in the documentation

[lthurner]

test coverage rate is now available on coveralls: https://coveralls.io/github/lthurner/pandapower?branch=master and is currently at 74%

The main holes in the coverage seem to be:

• coveralls does not seem to work with JIT (e.g. pypower_extension/create_J is marked as not tested even though it is)
• incomplete/missing tests for the toolbox
• incomplete tests for create functions
• incomplete tests for topology
• missing tests for diagnostic_reports (is this necessary? could also be excluded from coverage)

[lthurner]

coverage was moved to codecov, since coveralls was not working properly: https://codecov.io/github/lthurner/pandapower?branch=develop

Current coverage rate is at 87%