We have many places in our tests where we create temporary directories,
which we later remove (most of the time). We have at least 3 helpers to
do this, and various places where it's done ad-hoc (and the cleanup is
not always present).
To try to reduce the clutter, and make the tests more uniform and
readable, this patch introduces two helpers in a new "testutil" package:
one for creating and one for removing temporary directories.
These new functions are safer, better tested, and make the tests more
consistent. All the tests are updated to use them.
This patch extends WriteFile to allow arbitrary operations to be applied
to the file before it is atomically renamed.
This will be used in upcoming patches to change the mtime of the file
before it is atomically renamed.
This patch adds a new internal/safeio package, which is meant to implement
safer version of some I/O related functions.
For now, only an atomic version of ioutil.WriteFile is implemented. More may
be added later if there's a need for them.
