testers.testBuildFailure: Read last log line without final newline

pkgs/build-support/testers/expect-failure.sh

@@ -21,7 +21,7 @@ set -eu
 echo "testBuildFailure: Expecting non-zero exit from builder and args: ${*@Q}"
 
 ("$@" 2>&1) | @coreutils@/bin/tee $TMPDIR/testBuildFailure.log \
-  | while read ln; do
+  | while IFS= read -r ln; do
     echo "original builder: $ln"
   done
 

pkgs/build-support/testers/test/default.nix

@@ -29,15 +29,24 @@ lib.recurseIntoAttrs {
     happy = runCommand "testBuildFailure-happy" {
       failed = testers.testBuildFailure (runCommand "fail" {} ''
         echo ok-ish >$out
+
         echo failing though
         echo also stderr 1>&2
+        echo 'line\nwith-\bbackslashes'
+        printf "incomplete line - no newline"
+
         exit 3
       '');
     } ''
+      grep -F 'ok-ish' $failed/result
+
       grep -F 'failing though' $failed/testBuildFailure.log
       grep -F 'also stderr' $failed/testBuildFailure.log
-      grep -F 'ok-ish' $failed/result
+      grep -F 'line\nwith-\bbackslashes' $failed/testBuildFailure.log
+      grep -F 'incomplete line - no newline' $failed/testBuildFailure.log
+
       [[ 3 = $(cat $failed/testBuildFailure.exit) ]]
+
       touch $out
     '';