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, 5 insertions, 5 deletions

diff --git a/tests/check-refs.sh b/tests/check-refs.sh
index 65a72552a..2778e491d 100644
--- a/tests/check-refs.sh
+++ b/tests/check-refs.sh
@@ -8,14 +8,14 @@ dep=$(nix-build -o $RESULT check-refs.nix -A dep)
 
 # test1 references dep, not itself.
 test1=$(nix-build -o $RESULT check-refs.nix -A test1)
-(! nix-store -q --references $test1 | grep -q $test1)
-nix-store -q --references $test1 | grep -q $dep
+nix-store -q --references $test1 | grepQuietInverse $test1
+nix-store -q --references $test1 | grepQuiet $dep
 
 # test2 references src, not itself nor dep.
 test2=$(nix-build -o $RESULT check-refs.nix -A test2)
-(! nix-store -q --references $test2 | grep -q $test2)
-(! nix-store -q --references $test2 | grep -q $dep)
-nix-store -q --references $test2 | grep -q aux-ref
+nix-store -q --references $test2 | grepQuietInverse $test2
+nix-store -q --references $test2 | grepQuietInverse $dep
+nix-store -q --references $test2 | grepQuiet aux-ref
 
 # test3 should fail (unallowed ref).
 (! nix-build -o $RESULT check-refs.nix -A test3)