Instead of using -e, check for error explicitly and dump last lines from stderr log

debian/rules

@@ -1,12 +1,18 @@
 #!/bin/bash
 
-set -eu
+set -u
 set -o pipefail
 
 [ "$1" = binary ] || exit 0
 
 ./generate_testcases.sh | xargs --max-args=8 ./check.sh 2>../buildlog.txt | tee ../results.txt
 
+if [ $? -ne 0 ]; then
+	echo "Generating the testcases failed. The last 10 lines from the stderr log are:"
+	tail --lines=10 ../buildlog.txt
+	exit 1
+fi
+
 num_results=$(wc -l < ../results.txt)
 echo "Num-Testcases: $num_results"
 echo "Perc-All-Agree: $(echo "scale=2;$(grep -E ' 0 0 0$| 1 1 1$' ../results.txt | wc -l)*100/$num_results" | bc) %"