schematic test cases: exceptions for getters
schematic test cases: exceptions for type adders
schematic test cases: exceptions for node/connection adders and getters
schematic test cases: exceptions for constraints
reorganize the order of test cases to keep similar checks together
schematic test cases: explicit tests for all getters

because nontrivially unreachable cases can't be excluded from coverage,
this is about as comprehensive as the tests can get for Schematic
Merge branch 'master' into schematic-tests
Merge pull request #13 from mtrberzi/schematic-tests

Test cases for Schematic