`diff_test` doesn't show hidden whitespace characters

When using `diff_test`, it can be hard to determine why two files differ if the difference is due to whitespace (e.g. `^M` at the end of lines).

Would it be possible to add more configuration to `diff_test`? For example using `cat -A` to preprocess the files and/or passing `--strip-trailing-cr` to `diff`? Being able to enable color would also be helpful, although not directly related.