test-lib: redirect stdin of tests

We want to run tests in a predictable, sterile environment
so we can get repeatable results.  They should take as
little input as possible from the environment outside the
test script. We already sanitize environment variables, but
leave stdin untouched. This means that scripts can
accidentally be impacted by content on stdin, or whether
stdin isatty().

Furthermore, scripts reading from stdin can be annoying to
outer loops which care about their stdin offset, like:

  while read sha1; do
      make test
  done

A test which accidentally reads stdin would soak up all of
the rest of the input intended for the outer shell loop.

Let's redirect stdin from /dev/null, which solves both
of these problems. It won't detect tests accidentally
reading from stdin, but since doing so now gives a
deterministic result, we don't need to consider that an
error.

We'll also leave file descriptor 6 as a link to the original
stdin. Tests shouldn't need to look at this, but it can be
convenient for inserting interactive commands while
debugging tests (e.g., you could insert "bash <&6 >&3 2>&4"
to run interactive commands in the environment of the test
script).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/test-lib.sh b/t/test-lib.sh
index d7dfc8b0b1939180f16b8245e58465f883e85cbc..a73a77b3b62ee52127d97484899c6f3c18a68245 100644 (file)
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -191,6 +191,7 @@ then
 fi
 
 exec 5>&1
+exec 6<&0
 if test "$verbose" = "t"
 then
        exec 4>&2 3>&1
@@ -469,7 +470,7 @@ test_debug () {
 test_eval_ () {
        # This is a separate function because some tests use
        # "return" to end a test_expect_success block early.
-       eval >&3 2>&4 "$*"
+       eval </dev/null >&3 2>&4 "$*"
 }
 
 test_run_ () {