Improve the timeouts test

- More concise
- Also checks error messages
- Checks more error codes

The nature of that bug is that if the first command's exit status is
correctly 101 and not 1, the rest should be correctly 101, 100, etc.
too.

tests/functional/timeout.sh

@@ -7,39 +7,14 @@ source common.sh
 # XXX: This shouldn’t be, but #4813 cause this test to fail
 needLocalStore "see #4813"
 
-messages=$(nix-build -Q timeout.nix -A infiniteLoop --timeout 2 2>&1) && status=0 || status=$?
+# FIXME: https://github.com/NixOS/nix/issues/4813
+expectStderr 101 nix-build -Q timeout.nix -A infiniteLoop --timeout 2 | grepQuiet "timed out" \
+    || skipTest "Do not block CI until fixed"
 
-if [ "$status" -ne 101 ]; then
-    echo "error: 'nix-store' exited with '$status'; should have exited 101"
+expectStderr 1 nix-build -Q timeout.nix -A infiniteLoop --max-build-log-size 100 | grepQuiet "killed after writing more than 100 bytes of log output"
 
-    # FIXME: https://github.com/NixOS/nix/issues/4813
-    skipTest "Do not block CI until fixed"
+expectStderr 101 nix-build timeout.nix -A silent --max-silent-time 2 | grepQuiet "timed out after 2 seconds"
 
-    exit 1
-fi
+expectStderr 100 nix-build timeout.nix -A closeLog | grepQuiet "builder failed due to signal"
 
-if echo "$messages" | grepQuietInvert "timed out"; then
-    echo "error: build may have failed for reasons other than timeout; output:"
-    echo "$messages" >&2
-    exit 1
-fi
-
-if nix-build -Q timeout.nix -A infiniteLoop --max-build-log-size 100; then
-    echo "build should have failed"
-    exit 1
-fi
-
-if nix-build timeout.nix -A silent --max-silent-time 2; then
-    echo "build should have failed"
-    exit 1
-fi
-
-if nix-build timeout.nix -A closeLog; then
-    echo "build should have failed"
-    exit 1
-fi
-
-if nix build -f timeout.nix silent --max-silent-time 2; then
-    echo "build should have failed"
-    exit 1
-fi
+expectStderr 1 nix build -f timeout.nix silent --max-silent-time 2 | grepQuiet "timed out after 2 seconds"