gc: use randutil.NewTestRand() instead of hardcoded seed

Previously randomized tests used hardcoded sees 1 for testing.
This is giving us fixed coverage which can't find new failure modes.
This commit changes it to use randutil.NewTestRand() which uses
different seed by default, but could be overridden for failure
reproductions.

Release note: None

pkg/kv/kvserver/gc/BUILD.bazel

@@ -39,6 +39,7 @@ go_test(
         "gc_old_test.go",
         "gc_random_test.go",
         "gc_test.go",
+        "main_test.go",
     ],
     embed = [":gc"],
     deps = [

pkg/kv/kvserver/gc/gc_random_test.go

@@ -25,6 +25,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/protoutil"
+	"github.com/cockroachdb/cockroach/pkg/util/randutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -94,7 +95,6 @@ const intentAgeThreshold = 2 * time.Hour
 // implementation. It runs both the new and old implementation and ensures
 // that they produce exactly the same results on the same set of keys.
 func TestRunNewVsOld(t *testing.T) {
-	rng := rand.New(rand.NewSource(1))
 	ctx := context.Background()
 	const N = 100000
 
@@ -117,6 +117,9 @@ func TestRunNewVsOld(t *testing.T) {
 		},
 	} {
 		t.Run(fmt.Sprintf("%v@%v,ttlSec=%v", tc.ds, tc.now, tc.ttlSec), func(t *testing.T) {
+			rng, seed := randutil.NewTestRand()
+			t.Logf("Using subtest seed: %d", seed)
+
 			eng := storage.NewDefaultInMemForTesting()
 			defer eng.Close()
 
@@ -152,7 +155,6 @@ func TestRunNewVsOld(t *testing.T) {
 // BenchmarkRun benchmarks the old and implementations of Run with different
 // data distributions.
 func BenchmarkRun(b *testing.B) {
-	rng := rand.New(rand.NewSource(1))
 	ctx := context.Background()
 	runGC := func(eng storage.Engine, old bool, spec randomRunGCTestSpec) (Info, error) {
 		runGCFunc := Run
@@ -176,7 +178,7 @@ func BenchmarkRun(b *testing.B) {
 				return nil
 			})
 	}
-	makeTest := func(old bool, spec randomRunGCTestSpec) func(b *testing.B) {
+	makeTest := func(old bool, spec randomRunGCTestSpec, rng *rand.Rand) func(b *testing.B) {
 		return func(b *testing.B) {
 			eng := storage.NewDefaultInMemForTesting()
 			defer eng.Close()
@@ -207,8 +209,11 @@ func BenchmarkRun(b *testing.B) {
 	specs = append(specs, specsWithTTLs(lotsOfVersionsMidSizeRows, ts100, ttls)...)
 	for _, old := range []bool{true, false} {
 		b.Run(fmt.Sprintf("old=%v", old), func(b *testing.B) {
+			rng, seed := randutil.NewTestRand()
+			b.Logf("Using benchmark seed: %d", seed)
+
 			for _, spec := range specs {
-				b.Run(fmt.Sprint(spec.ds), makeTest(old, spec))
+				b.Run(fmt.Sprint(spec.ds), makeTest(old, spec, rng))
 			}
 		})
 	}
@@ -254,7 +259,9 @@ func TestNewVsInvariants(t *testing.T) {
 		},
 	} {
 		t.Run(fmt.Sprintf("%v@%v,ttl=%vsec", tc.ds, tc.now, tc.ttlSec), func(t *testing.T) {
-			rng := rand.New(rand.NewSource(1))
+			rng, seed := randutil.NewTestRand()
+			t.Logf("Using subtest seed: %d", seed)
+
 			desc := tc.ds.desc()
 			eng := storage.NewDefaultInMemForTesting()
 			defer eng.Close()

pkg/kv/kvserver/gc/main_test.go

@@ -0,0 +1,23 @@
+// Copyright 2022 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+package gc
+
+import (
+	"os"
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/util/randutil"
+)
+
+func TestMain(m *testing.M) {
+	randutil.SeedForTests()
+	os.Exit(m.Run())
+}