wwtest: bounded package concurrency via exec start/poll

test/package/package_test.ww

@@ -492,6 +492,19 @@ fn packagepath(relative: str) str = {
 	assert(!has(outc.stdout, ".hidden"));
 	assert(!has(outc.stdout, "_skip"));
 
+	// Concurrent scheduling must not reorder the emitted byte stream.
+	let seq: str = strings.dup(outc.stdout);
+	let j4: []str = [driver("ww"), "test", "-j", "4", spec];
+	runcommand(root, "tree-j4", j4,
+		(30i64 * (time.second: i64)): time.duration, &outc);
+	expectexit(&outc, 0);
+	assert(same(outc.stdout, seq));
+
+	let j0: []str = [driver("ww"), "test", "-j", "0", spec];
+	runcommand(root, "tree-j0", j0, time.second, &outc);
+	expectexit(&outc, 2);
+	assert(has(outc.stderr, "usage: wwtest package"));
+
 	let patc: []str = [driver("ww"), "test", spec, "glob*"];
 	let patw: []str = [driver("ww_ww"), "test", spec, "glob*"];
 	runcommand(root, "tree-pattern-c", patc, time.second, &outc);