add a test that verifies adding an edge works
add a test that verifies adding an edge works

yeah, this didn't work and so I added a test, it was due to the lack of hash
code override

Signed-off-by: Sam Phippen <e5a09176608998a68778e11d5021c871e8fae93c@googlemail.com>

samphippen/spe,samphippen/spe,samphippen/spe,samphippen/spe