t0030: encapsulate ipfs mount

As described in issue #1109 on OSX some output from
test_must_fail unfortunately goes into the "output"
file that we use to test the output from "ipfs mount".

This patch avoids the above by encapsulating the call
to "ipfs mount" into a temporary function.

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

test/sharness/t0030-mount.sh

@@ -21,7 +21,8 @@ test_launch_ipfs_daemon
 #  test mount failure before mounting properly.
 
 test_expect_success "'ipfs mount' fails when there is no mount dir" '
-	test_must_fail ipfs mount -f=not_ipfs -n=not_ipns >output 2>output.err
+	tmp_ipfs_mount() { ipfs mount -f=not_ipfs -n=not_ipns >output 2>output.err; } &&
+	test_must_fail tmp_ipfs_mount
 '
 
 test_expect_failure "'ipfs mount' output looks good" '