Comment 3 for bug 681125

It appears that the problem is that PackageUpload.getSourceBuild only returns non-None if the upload succeeded. The tests of build failure emails must therefore have inaccurate test fixtures.

It's not clear to me whether there's another way to get the source build that would work in this context. bigjools suggests that build-based uploads can be detected because they will always have None for PackageUpload.signing_key, but using this check causes test failures.