When installing the ATH on osx, some users see this type of error:
Installing the required dependencies on OSX is not documented (and past techniques don't seem to work on fresh installs). This seems required by nodegit only.
Nodegit has also been a problem (see Vivek Pandey) with failures with signatures (still trying to get the specific error message for that). Nodegit is presumably used to test multibranch (the equivalent in unit test code doesn't have this problem, it also uses a git client but doesn't seem as problematic as nodegit). Perhaps nodegit should be replaced with direct calls to the git client via shell scripting (given that seems to be mostly what it does anyway).