Add helper script for test reduction

tools/reduce_tests.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# A helper script to use multidelta to reduce to a minimal set of tests to
+# reproduce a failure.
+# Sometimes the tests interact in unexpected ways, so you need to run two
+# or three tests in order to cause the failure to occur.  It's tiresome to
+# determine a minimal subset of tests by hand; this script automates it.
+
+# I think https://github.com/DRMacIver/structureshrink would be better than
+# multidelta for this; multidelta requires strange workarounds.  But
+# multidelta is readily available in most distributions' packages, so using
+# that.
+
+set -ue
+
+if ! which multidelta &>/dev/null
+then
+    echo "multidelta not found.  Please install it to use this script" >&2
+    exit 1
+fi
+
+if [ $# != 1 ]
+then
+    printf "Usage: %s RNG_SEED\n" "$0" >&2
+    exit 1
+fi
+
+if [ ! -x tests/cata_test ]
+then
+    printf "Please build cata_test and run this script from the top-level directory" >&2
+    exit 1
+fi
+
+export rng_seed=$1
+
+# For some reason the following cata_test command returns 140, rather than 0 (success).
+# Not sure why.
+
+# We have to add braces around the lines to avoid topformflat messing up the file.
+# The braces are removed again inside our helper script.
+./tests/cata_test --list-test-names-only '~[.]' | \
+    grep '[^ ]' | sed 's/.*/{&}/' > list_of_tests || true
+multidelta tools/reduce_tests_helper.sh list_of_tests
+
+# vim:tw=0

tools/reduce_tests_helper.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Helper script for reduce_tests.sh
+
+set -uex
+
+# Disallow empty test list
+if [ ! -s "$multidelta_all_files" ]
+then
+    exit 1
+fi
+
+if ./tests/cata_test -d yes --abort --rng-seed "$rng_seed" \
+    -f <(tr -d '{}' < "$multidelta_all_files")
+then
+    exit 1
+fi
+
+exit 0