Compute the DAG of SCCs and check if it is a path

[sebschmi]

When assembling simulated linear unidirected reads without errors or missing coverage, the DAG of SCCs of the assembly graph should be a path. Otherwise, something somewhere went wrong.

• compute DAG of SCCs
• check if graph is a path
• include the whole check into the verify command
• output the DAG of SCCs in some common graph drawing format
• use some software to draw the DAG of SCCs in the pipeline

Test

• compute DAG of SCCs: empty graph
• compute DAG of SCCs: SCC
• compute DAG of SCCs: two WCCs that are SC
• compute DAG of SCCs: a WC graph with multiple SCCs that form a DAG that is not a path
• check if graph is a path: empty graph
• check if graph is a path: path
• check if graph is a path: single node
• check if graph is a path: single node with loop
• check if graph is a path: path with loop
• check if graph is a path: cycle
• check if graph is a path: path with backwards arc