I just spent a few hours banging my head on this one but it appears that my local git configuration was the source of a Fixture::FormatError occurring while running tests in Rails.

The specific error looked like this:

Fixture::FormatError: a YAML error occurred parsing /dev/current/myapp/test/fixtures/blogs.yml.
Please note that YAML must be consistently indented using spaces. Tabs are not allowed.
Please have a look at http://www.yaml.org/faq.html
The exact error was:
  ArgumentError: Anonymous modules have no name to be referenced by

I have not yet pin pointed (and may never pin point) the exact source of the problem but what appears to have been causing it was my local git configuration (~/.gitconfig) which included the following two lines:

[core]
    whitespace = fix,-indent-with-non-tab,trailing-space,cr-at-eol

The git config file was passed around during a Cincinnati Ruby Brigade meeting and, being a git noob, I installed it dutifully.

Anyway, removing those two lines from the .gitconfig file resolved the issue after I moved the existing clone aside and re-cloned the repository. Feel free to provide details in the comments if you’ve got a clue and/or can shed some light on the exact cause.