plan tests 4

## Test if GFA files can be read
## Graph has the correct number of edges
## Graph has the correct number of nodes
## Check that the paths are correct


## Test if GFA files can be written
## Check that path's appear correctly
## Check that all nodes appear correctly
## Test that headers are produced, with the correct version
## Check that all edges appear correctly


## Check that sort produces the right output
## Check that 

