Properly clean up subprocesses in tests

Relying on the process group to figure out which processes to treat
as children and grandchildren of the test run was not correct, as
the testrunner didn't ensure it was creating a new process group.

When running inside 'make check' the process group was actually that
of make, not testrunner.sh.

Since setpgid is not universally available, we iterate the process
tree via ps, and kill the children recursively.

testrunner.sh

@@ -134,7 +134,7 @@ function testrunner::run_tests() {
     done
 
     if testrunner::function_declared teardown; then
-        teardown >>$test_output_file 2>&1
+        teardown >>$test_output_file
     fi
 
     [[ $DEBUG -eq 1 ]] && testrunner::print_test_output "Teardown"
@@ -210,14 +210,27 @@ function testrunner::print_test_output {
     fi
 }
 
-function testrunner::signal_children() {
-    signal=${1:-KILL}
-    child_pids=($(ps -o pid= -g $$ | sort --reverse))
-    # Remove first three (ps in subshell) and last (self)
-    child_pids=("${child_pids[@]:3:${#child_pids[@]}-4}")
-    for pid in "${child_pids[@]}"; do
-        echo "Sending $signal to PID $pid ($(ps -o command= $pid))"
-        kill -s $signal $pid >/dev/null 2>&1
+function testrunner::signal_children()
+{
+    local signal=${1:-TERM}
+    local pid=${2:-${BASHPID:-$$}}
+
+    local child_pids=()
+
+    IFS=
+    res=$(ps -o ppid,pid)
+    unset IFS
+    {
+        read # Skip header
+        while IFS=' ' read -r ppid cpid; do
+            test $ppid -eq $pid && child_pids+=($cpid)
+        done
+    }<<<"$res"
+
+    local p
+    for p in "${child_pids[@]}"; do
+        testrunner::signal_children $signal $p
+        kill -$signal $p >/dev/null 2>&1
     done
 }
 
@@ -276,7 +289,7 @@ for testsuite in "${testsuites[@]}"; do
         printf "tests_total+=${tests_total}; tests_failed+=${tests_failed}" >&3
 
         # Clean up if test didn't do it
-        testrunner::signal_children TERM >&2
+        testrunner::signal_children TERM
     )
     exec 4>&-
     if [[ $interrupted -eq 1 ]]; then