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, 2 deletions

diff --git a/tests/linux-sandbox.sh b/tests/linux-sandbox.sh
index e62039567..5667000d9 100644
--- a/tests/linux-sandbox.sh
+++ b/tests/linux-sandbox.sh
@@ -35,8 +35,8 @@ nix-build dependencies.nix --no-out-link --check --sandbox-paths /nix/store
 nix-build check.nix -A nondeterministic --sandbox-paths /nix/store --no-out-link
 
 (! nix-build check.nix -A nondeterministic --sandbox-paths /nix/store --no-out-link --check -K 2> $TEST_ROOT/log)
-if grep -q 'error: renaming' $TEST_ROOT/log; then false; fi
-grep -q 'may not be deterministic' $TEST_ROOT/log
+if grepQuiet 'error: renaming' $TEST_ROOT/log; then false; fi
+grepQuiet 'may not be deterministic' $TEST_ROOT/log
 
 # Test that sandboxed builds cannot write to /etc easily
 (! nix-build -E 'with import ./config.nix; mkDerivation { name = "etc-write"; buildCommand = "echo > /etc/test"; }' --no-out-link --sandbox-paths /nix/store)