Actually, wait a moment... looking at numpy/testing/nosetester.py, this comment in the README is just wrong, I think. By default in released versions, the tests do *not* fail on any warnings, and in develop versions, they do. And the `-Wd` option is ignored in any case (we always call `warnings.resetwarnings()` before running the tests, which wipes out any `-Wd` options).

It looks like once upon a time (see d93d0214eaec2cd45119ad1f7485e5628faffc2a), we suggested that people use `-Wd` to turn on fail-on-deprecation for their first run of the test suite after upgrading. I have no idea why we did that -- it makes sense that they might want to test *their* code with deprecation warnings on before upgrading, but why test numpy that way? If there is some reason, though, then the way they should do that now is something like
```
python -c "import numpy; numpy.test(raise_warnings=(DeprecationWarning,))'
```
Alternatively, if the defaults are good (which seems accurate to me), we should just delete these comments entirely.