Harden tests' bash

Use `set -u` and `set -o pipefail` to catch accidental mistakes and
failures more strongly.

 - `set -u` catches the use of undefined variables
 - `set -o pipefail` catches failures (like `set -e`) earlier in the
   pipeline.

This makes the tests a bit more robust. It is nice to read code not
worrying about these spurious success paths (via uncaught) errors
undermining the tests. Indeed, I caught some bugs doing this.

There are a few tests where we run a command that should fail, and then
search its output to make sure the failure message is one that we
expect. Before, since the `grep` was the last command in the pipeline
the exit code of those failing programs was silently ignored. Now with
`set -o pipefail` it won't be, and we have to do something so the
expected failure doesn't accidentally fail the test.

To do that we use `expect` and a new `expectStderr` to check for the
exact failing exit code. See the comments on each for why.

`grep -q` is replaced with `grepQuiet`, see the comments on that
function for why.

`grep -v` when we just want the exit code is replaced with `grepInverse,
see the comments on that function for why.

`grep -q -v` together is, surprise surprise, replaced with
`grepQuietInverse`, which is both combined.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/tests/timeout.sh b/tests/timeout.sh
index e3fb3ebcc..b179b79a2 100644
--- a/tests/timeout.sh
+++ b/tests/timeout.sh
@@ -5,17 +5,14 @@ source common.sh
 # XXX: This shouldn’t be, but #4813 cause this test to fail
 needLocalStore "see #4813"
 
-set +e
-messages=$(nix-build -Q timeout.nix -A infiniteLoop --timeout 2 2>&1)
-status=$?
-set -e
+messages=$(nix-build -Q timeout.nix -A infiniteLoop --timeout 2 2>&1) && status=0 || status=$?
 
 if [ $status -ne 101 ]; then
     echo "error: 'nix-store' exited with '$status'; should have exited 101"
     exit 1
 fi
 
-if ! echo "$messages" | grep -q "timed out"; then
+if echo "$messages" | grepQuietInvert "timed out"; then
     echo "error: build may have failed for reasons other than timeout; output:"
     echo "$messages" >&2
     exit 1