`fstab.configure`
=================

The `fstab.configure` extension appends text to the `/etc/fstab` from
environment variables beginning with `FSTAB_`. It also sets the
ownership and permissions of the file.

The first thing to test is that the extension doesn't write anything
if not requested to do so, but does create the file if it doesn't
exist.

    SCENARIO fstab.configure does nothing by default
    GIVEN a directory called tree/etc
    WHEN fstab.configure is run against tree
    THEN file tree/etc/fstab exists
    AND file tree/etc/fstab has permissions -rw-r--r--
    AND file tree/etc/fstab is owned by uid 0
    AND file tree/etc/fstab is owned by gid 0
    AND file tree/etc/fstab is empty

Append a something to the file, and verify the contents are exactly
correct.

    SCENARIO fstab.configure appends requested lines
    GIVEN a directory called tree/etc
    AND an environment variable FSTAB_FOO containing "foo"
    WHEN fstab.configure is run against tree
    THEN file tree/etc/fstab exists
    AND file tree/etc/fstab has permissions -rw-r--r--
    AND file tree/etc/fstab is owned by uid 0
    AND file tree/etc/fstab is owned by gid 0
    AND file tree/etc/fstab contains "foo\n"

Append something to an existing file, with wrong ownership and
permission.

    SCENARIO fstab.configure appends to existing file
    GIVEN a directory called tree/etc
    AND a file called tree/etc/fstab containing "# comment\n"
    AND tree/etc/fstab is owned by uid 1
    AND tree/etc/fstab is owned by gid 1
    AND tree/etc/fstab has permissions 0600
    AND an environment variable FSTAB_FOO containing "foo"
    WHEN fstab.configure is run against tree
    THEN file tree/etc/fstab exists
    AND file tree/etc/fstab has permissions -rw-r--r--
    AND file tree/etc/fstab is owned by uid 0
    AND file tree/etc/fstab is owned by gid 0
    AND file tree/etc/fstab contains "# comment\nfoo\n"

Implement running `fstab.configure`
-----------------------------------

When we actually run `fstab.configure`, we source `$DATADIR/env` to
get the desired environment variables.

    IMPLEMENTS WHEN fstab.configure is run against (\S+)
    if [ -e "$DATADIR/env" ]
    then
        . "$DATADIR/env"
    fi
    "$SRCDIR/morphlib/exts/fstab.configure" "$DATADIR/$MATCH_1"