unordered_map is unordered (O.o) so it cannot be compared
by two simultaneous iterators

+ fix unused variables warning

+ added tests

Primitive doesn't work well in algorithms. Also, almost (?) all
algorithms are working with integer values on nodes/edges, so this
should be just fine.

Also simplify lambdas in tests to capture everything

Also simplify lambdas in tests to capture everything

Helps to track failures

It now stores number of edges, instead of just bool indicating
that there is an edge

Also edited to use ASSERT_EQUAL for better fail messages