scheduler_perf: work around incorrect gotestsum failure reports

Because Go does not a "pass" action for
benchmarks (golang/go#66825 (comment)),
gotestsum reports a successful benchmark run as failed
(gotestyourself/gotestsum#413 (comment)).

We can work around that in each benchmark and sub-benchmark by emitting the
output line that `go test` expects on stdout from the test binary for success.

test/integration/scheduler_perf/scheduler_perf.go

@@ -29,6 +29,7 @@ import (
 	"os"
 	"path"
 	"regexp"
+	"slices"
 	"strings"
 	"sync"
 	"testing"
@@ -1115,6 +1116,32 @@ func featureGatesMerge(src map[featuregate.Feature]bool, overrides map[featurega
 	return result
 }
 
+// fixJSONOutput works around Go not emitting a "pass" action for
+// sub-benchmarks
+// (https://github.com/golang/go/issues/66825#issuecomment-2343229005), which
+// causes gotestsum to report a successful benchmark run as failed
+// (https://github.com/gotestyourself/gotestsum/issues/413#issuecomment-2343206787).
+//
+// It does this by printing the missing "PASS" output line that test2json
+// then converts into the "pass" action.
+func fixJSONOutput(b *testing.B) {
+	if !slices.Contains(os.Args, "-test.v=test2json") {
+		// Not printing JSON.
+		return
+	}
+
+	start := time.Now()
+	b.Cleanup(func() {
+		if b.Failed() {
+			// Really has failed, do nothing.
+			return
+		}
+		// SYN gets injected when using -test.v=test2json, see
+		// https://cs.opensource.google/go/go/+/refs/tags/go1.23.3:src/testing/testing.go;drc=87ec2c959c73e62bfae230ef7efca11ec2a90804;l=527
+		fmt.Fprintf(os.Stderr, "%c--- PASS: %s (%.2fs)\n", 22 /* SYN */, b.Name(), time.Since(start).Seconds())
+	})
+}
+
 // RunBenchmarkPerfScheduling runs the scheduler performance benchmark tests.
 //
 // You can pass your own scheduler plugins via outOfTreePluginRegistry.
@@ -1128,6 +1155,7 @@ func RunBenchmarkPerfScheduling(b *testing.B, configFile string, topicName strin
 	if err = validateTestCases(testCases); err != nil {
 		b.Fatal(err)
 	}
+	fixJSONOutput(b)
 
 	if testing.Short() {
 		PerfSchedulingLabelFilter += ",+short"
@@ -1147,11 +1175,13 @@ func RunBenchmarkPerfScheduling(b *testing.B, configFile string, topicName strin
 	dataItems := DataItems{Version: "v1"}
 	for _, tc := range testCases {
 		b.Run(tc.Name, func(b *testing.B) {
+			fixJSONOutput(b)
 			for _, w := range tc.Workloads {
 				b.Run(w.Name, func(b *testing.B) {
 					if !enabled(testcaseLabelSelectors, append(tc.Labels, w.Labels...)...) {
 						b.Skipf("disabled by label filter %q", PerfSchedulingLabelFilter)
 					}
+					fixJSONOutput(b)
 
 					featureGates := featureGatesMerge(tc.FeatureGates, w.FeatureGates)
 					informerFactory, tCtx := setupTestCase(b, tc, featureGates, output, outOfTreePluginRegistry)