testing: add -shuffle=off|on|N to alter the execution order of tests and benchmarks

This CL adds a new flag to the testing package and the go test command
which randomizes the execution order for tests and benchmarks.
This can be useful for identifying unwanted dependencies
between test or benchmark functions.
The flag is off by default. If `-shuffle` is set to `on` then the system
clock will be used as the seed value. If `-shuffle` is set to an integer
N, then N will be used as the seed value. In both cases, the seed will
be reported for failed runs so that they can reproduced later on.

Fixes #28592

Change-Id: I62e7dfae5f63f97a0cbd7830ea844d9f7beac335
Reviewed-on: https://go-review.googlesource.com/c/go/+/310033
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Bryan C. Mills <bcmills@google.com>

10 files changed, 249 insertions, 4 deletions

diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 103eecf79c..0a12eaf4e9 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -2667,6 +2667,13 @@
 // 	    the Go tree can run a sanity check but not spend time running
 // 	    exhaustive tests.
 //
+// 	-shuffle off,on,N
+// 		Randomize the execution order of tests and benchmarks.
+// 		It is off by default. If -shuffle is set to on, then it will seed
+// 		the randomizer using the system clock. If -shuffle is set to an
+// 		integer N, then N will be used as the seed value. In both cases,
+// 		the seed will be reported for reproducibility.
+//
 // 	-timeout d
 // 	    If a test binary runs longer than duration d, panic.
 // 	    If d is 0, the timeout is disabled.
diff --git a/src/cmd/go/internal/test/flagdefs.go b/src/cmd/go/internal/test/flagdefs.go
index 8a0a07683b..37ac81c267 100644
--- a/src/cmd/go/internal/test/flagdefs.go
+++ b/src/cmd/go/internal/test/flagdefs.go
@@ -28,6 +28,7 @@ var passFlagToTest = map[string]bool{
 	"parallel":             true,
 	"run":                  true,
 	"short":                true,
+	"shuffle":              true,
 	"timeout":              true,
 	"trace":                true,
 	"v":                    true,
diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index 847b9357b4..c2f8aed004 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -272,6 +272,13 @@ control the execution of any test:
 	    the Go tree can run a sanity check but not spend time running
 	    exhaustive tests.
 
+	-shuffle off,on,N
+		Randomize the execution order of tests and benchmarks.
+		It is off by default. If -shuffle is set to on, then it will seed
+		the randomizer using the system clock. If -shuffle is set to an
+		integer N, then N will be used as the seed value. In both cases,
+		the seed will be reported for reproducibility.
+
 	-timeout d
 	    If a test binary runs longer than duration d, panic.
 	    If d is 0, the timeout is disabled.
@@ -480,6 +487,7 @@ var (
 	testList         string                            // -list flag
 	testO            string                            // -o flag
 	testOutputDir    = base.Cwd                        // -outputdir flag
+	testShuffle      shuffleFlag                       // -shuffle flag
 	testTimeout      time.Duration                     // -timeout flag
 	testV            bool                              // -v flag
 	testVet          = vetFlag{flags: defaultVetFlags} // -vet flag
diff --git a/src/cmd/go/internal/test/testflag.go b/src/cmd/go/internal/test/testflag.go
index 10e6604da5..6ed96a36d0 100644
--- a/src/cmd/go/internal/test/testflag.go
+++ b/src/cmd/go/internal/test/testflag.go
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"time"
 
@@ -68,6 +69,7 @@ func init() {
 	cf.DurationVar(&testTimeout, "timeout", 10*time.Minute, "")
 	cf.StringVar(&testTrace, "trace", "", "")
 	cf.BoolVar(&testV, "v", false, "")
+	cf.Var(&testShuffle, "shuffle", "")
 
 	for name, _ := range passFlagToTest {
 		cf.Var(cf.Lookup(name).Value, "test."+name, "")
@@ -194,6 +196,41 @@ func (f *vetFlag) Set(value string) error {
 	return nil
 }
 
+type shuffleFlag struct {
+	on   bool
+	seed *int64
+}
+
+func (f *shuffleFlag) String() string {
+	if !f.on {
+		return "off"
+	}
+	if f.seed == nil {
+		return "on"
+	}
+	return fmt.Sprintf("%d", *f.seed)
+}
+
+func (f *shuffleFlag) Set(value string) error {
+	if value == "off" {
+		*f = shuffleFlag{on: false}
+		return nil
+	}
+
+	if value == "on" {
+		*f = shuffleFlag{on: true}
+		return nil
+	}
+
+	seed, err := strconv.ParseInt(value, 10, 64)
+	if err != nil {
+		return fmt.Errorf(`-shuffle argument must be "on", "off", or an int64: %v`, err)
+	}
+
+	*f = shuffleFlag{on: true, seed: &seed}
+	return nil
+}
+
 // testFlags processes the command line, grabbing -x and -c, rewriting known flags
 // to have "test" before them, and reading the command line for the test binary.
 // Unfortunately for us, we need to do our own flag processing because go test
diff --git a/src/cmd/go/testdata/script/test_shuffle.txt b/src/cmd/go/testdata/script/test_shuffle.txt
new file mode 100644
index 0000000000..3a50605c34
--- /dev/null
+++ b/src/cmd/go/testdata/script/test_shuffle.txt
@@ -0,0 +1,148 @@
+# Shuffle order of tests and benchmarks
+
+# Run tests
+go test -v foo_test.go
+! stdout '-test.shuffle '
+stdout '(?s)TestOne(.*)TestTwo(.*)TestThree'
+
+go test -v -shuffle=off foo_test.go
+! stdout '-test.shuffle '
+stdout '(?s)TestOne(.*)TestTwo(.*)TestThree'
+
+go test -v -shuffle=42 foo_test.go
+stdout '^-test.shuffle 42'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo'
+
+go test -v -shuffle=43 foo_test.go
+stdout '^-test.shuffle 43'
+stdout '(?s)TestThree(.*)TestTwo(.*)TestOne'
+
+go test -v -shuffle=44 foo_test.go
+stdout '^-test.shuffle 44'
+stdout '(?s)TestOne(.*)TestThree(.*)TestTwo'
+
+go test -v -shuffle=0 foo_test.go
+stdout '^-test.shuffle 0'
+stdout '(?s)TestTwo(.*)TestOne(.*)TestThree'
+
+go test -v -shuffle -1 foo_test.go
+stdout '^-test.shuffle -1'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo'
+
+go test -v -shuffle=on foo_test.go
+stdout '^-test.shuffle '
+stdout '(?s)=== RUN   TestOne(.*)--- PASS: TestOne'
+stdout '(?s)=== RUN   TestTwo(.*)--- PASS: TestTwo'
+stdout '(?s)=== RUN   TestThree(.*)--- PASS: TestThree'
+
+
+# Run tests and benchmarks
+go test -v -bench=. foo_test.go
+! stdout '-test.shuffle '
+stdout '(?s)TestOne(.*)TestTwo(.*)TestThree(.*)BenchmarkOne(.*)BenchmarkTwo(.*)BenchmarkThree'
+
+go test -v -bench=. -shuffle=off foo_test.go
+! stdout '-test.shuffle '
+stdout '(?s)TestOne(.*)TestTwo(.*)TestThree(.*)BenchmarkOne(.*)BenchmarkTwo(.*)BenchmarkThree'
+
+go test -v -bench=. -shuffle=42 foo_test.go
+stdout '^-test.shuffle 42'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo(.*)BenchmarkThree(.*)BenchmarkOne(.*)BenchmarkTwo'
+
+go test -v -bench=. -shuffle=43 foo_test.go
+stdout '^-test.shuffle 43'
+stdout '(?s)TestThree(.*)TestTwo(.*)TestOne(.*)BenchmarkThree(.*)BenchmarkOne(.*)BenchmarkTwo'
+
+go test -v -bench=. -shuffle=44 foo_test.go
+stdout '^-test.shuffle 44'
+stdout '(?s)TestOne(.*)TestThree(.*)TestTwo(.*)BenchmarkTwo(.*)BenchmarkOne(.*)BenchmarkThree'
+
+go test -v -bench=. -shuffle=0 foo_test.go
+stdout '^-test.shuffle 0'
+stdout '(?s)TestTwo(.*)TestOne(.*)TestThree(.*)BenchmarkThree(.*)BenchmarkOne(.*)BenchmarkTwo'
+
+go test -v -bench=. -shuffle -1 foo_test.go
+stdout '^-test.shuffle -1'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo(.*)BenchmarkOne(.*)BenchmarkThree(.*)BenchmarkTwo'
+
+go test -v -bench=. -shuffle=on foo_test.go
+stdout '^-test.shuffle '
+stdout '(?s)=== RUN   TestOne(.*)--- PASS: TestOne'
+stdout '(?s)=== RUN   TestTwo(.*)--- PASS: TestTwo'
+stdout '(?s)=== RUN   TestThree(.*)--- PASS: TestThree'
+stdout -count=2 'BenchmarkOne'
+stdout -count=2 'BenchmarkTwo'
+stdout -count=2 'BenchmarkThree'
+
+
+# When running go test -count=N, each of the N runs distinct runs should maintain the same
+# shuffled order of these tests.
+go test -v -shuffle=43 -count=4 foo_test.go
+stdout '^-test.shuffle 43'
+stdout '(?s)TestThree(.*)TestTwo(.*)TestOne(.*)TestThree(.*)TestTwo(.*)TestOne(.*)TestThree(.*)TestTwo(.*)TestOne(.*)TestThree(.*)TestTwo(.*)TestOne'
+
+go test -v -bench=. -shuffle=44 -count=2 foo_test.go
+stdout '^-test.shuffle 44'
+stdout '(?s)TestOne(.*)TestThree(.*)TestTwo(.*)TestOne(.*)TestThree(.*)TestTwo(.*)BenchmarkTwo(.*)BenchmarkOne(.*)BenchmarkThree(.*)'
+
+
+# The feature should work with test binaries as well
+go test -c
+exec ./m.test -test.shuffle=off
+! stdout '^-test.shuffle '
+
+exec ./m.test -test.shuffle=on
+stdout '^-test.shuffle '
+
+exec ./m.test -test.v -test.bench=. -test.shuffle=0 foo_test.go
+stdout '^-test.shuffle 0'
+stdout '(?s)TestTwo(.*)TestOne(.*)TestThree(.*)BenchmarkThree(.*)BenchmarkOne(.*)BenchmarkTwo'
+
+exec ./m.test -test.v -test.bench=. -test.shuffle=123 foo_test.go
+stdout '^-test.shuffle 123'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo(.*)BenchmarkThree(.*)BenchmarkTwo(.*)BenchmarkOne'
+
+exec ./m.test -test.v -test.bench=. -test.shuffle=-1 foo_test.go
+stdout '^-test.shuffle -1'
+stdout '(?s)TestThree(.*)TestOne(.*)TestTwo(.*)BenchmarkOne(.*)BenchmarkThree(.*)BenchmarkTwo'
+
+exec ./m.test -test.v -test.bench=. -test.shuffle=44 -test.count=2 foo_test.go
+stdout '^-test.shuffle 44'
+stdout '(?s)TestOne(.*)TestThree(.*)TestTwo(.*)TestOne(.*)TestThree(.*)TestTwo(.*)BenchmarkTwo(.*)BenchmarkOne(.*)BenchmarkThree(.*)'
+
+
+# Negative testcases for invalid input
+! go test -shuffle -count=2
+stderr 'invalid value "-count=2" for flag -shuffle: -shuffle argument must be "on", "off", or an int64: strconv.ParseInt: parsing "-count=2": invalid syntax'
+
+! go test -shuffle=
+stderr '(?s)invalid value "" for flag -shuffle: -shuffle argument must be "on", "off", or an int64: strconv.ParseInt: parsing "": invalid syntax'
+
+! go test -shuffle=' '
+stderr '(?s)invalid value " " for flag -shuffle: -shuffle argument must be "on", "off", or an int64: strconv.ParseInt: parsing " ": invalid syntax'
+
+! go test -shuffle=true
+stderr 'invalid value "true" for flag -shuffle: -shuffle argument must be "on", "off", or an int64: strconv.ParseInt: parsing "true": invalid syntax'
+
+! go test -shuffle='abc'
+stderr 'invalid value "abc" for flag -shuffle: -shuffle argument must be "on", "off", or an int64: strconv.ParseInt: parsing "abc": invalid syntax'
+
+-- go.mod --
+module m
+
+go 1.16
+-- foo_test.go --
+package foo
+
+import "testing"
+
+func TestOne(t *testing.T)   {}
+func TestTwo(t *testing.T)   {}
+func TestThree(t *testing.T) {}
+
+func BenchmarkOne(b *testing.B)   {}
+func BenchmarkTwo(b *testing.B)   {}
+func BenchmarkThree(b *testing.B) {}
+
+-- foo.go --
+package foo
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 1b93348edb..9cdfb898ba 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -503,7 +503,7 @@ var depsRules = `
 	FMT, flag, math/rand
 	< testing/quick;
 
-	FMT, flag, runtime/debug, runtime/trace, internal/sysinfo
+	FMT, flag, runtime/debug, runtime/trace, internal/sysinfo, math/rand
 	< testing;
 
 	internal/testlog, runtime/pprof, regexp
diff --git a/src/math/rand/export_test.go b/src/math/rand/export_test.go
new file mode 100644
index 0000000000..560010be6b
--- /dev/null
+++ b/src/math/rand/export_test.go
@@ -0,0 +1,17 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rand
+
+func Int31nForTest(r *Rand, n int32) int32 {
+	return r.int31n(n)
+}
+
+func GetNormalDistributionParameters() (float64, [128]uint32, [128]float32, [128]float32) {
+	return rn, kn, wn, fn
+}
+
+func GetExponentialDistributionParameters() (float64, [256]uint32, [256]float32, [256]float32) {
+	return re, ke, we, fe
+}
diff --git a/src/math/rand/race_test.go b/src/math/rand/race_test.go
index 186c7169d8..e7d103664b 100644
--- a/src/math/rand/race_test.go
+++ b/src/math/rand/race_test.go
@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package rand
+package rand_test
 
 import (
+	. "math/rand"
 	"sync"
 	"testing"
 )
diff --git a/src/math/rand/rand_test.go b/src/math/rand/rand_test.go
index e037aaed0e..462de8b73b 100644
--- a/src/math/rand/rand_test.go
+++ b/src/math/rand/rand_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package rand
+package rand_test
 
 import (
 	"bytes"
@@ -11,6 +11,7 @@ import (
 	"internal/testenv"
 	"io"
 	"math"
+	. "math/rand"
 	"os"
 	"runtime"
 	"testing"
@@ -21,6 +22,9 @@ const (
 	numTestSamples = 10000
 )
 
+var rn, kn, wn, fn = GetNormalDistributionParameters()
+var re, ke, we, fe = GetExponentialDistributionParameters()
+
 type statsResults struct {
 	mean        float64
 	stddev      float64
@@ -503,7 +507,7 @@ func TestUniformFactorial(t *testing.T) {
 				fn   func() int
 			}{
 				{name: "Int31n", fn: func() int { return int(r.Int31n(int32(nfact))) }},
-				{name: "int31n", fn: func() int { return int(r.int31n(int32(nfact))) }},
+				{name: "int31n", fn: func() int { return int(Int31nForTest(r, int32(nfact))) }},
 				{name: "Perm", fn: func() int { return encodePerm(r.Perm(n)) }},
 				{name: "Shuffle", fn: func() int {
 					// Generate permutation using Shuffle.
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 1562eadef0..85a7fec65f 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -242,6 +242,7 @@ import (
 	"fmt"
 	"internal/race"
 	"io"
+	"math/rand"
 	"os"
 	"runtime"
 	"runtime/debug"
@@ -299,6 +300,7 @@ func Init() {
 	cpuListStr = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
 	parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
 	testlog = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
+	shuffle = flag.String("test.shuffle", "off", "randomize the execution order of tests and benchmarks")
 
 	initBenchmarkFlags()
 }
@@ -325,6 +327,7 @@ var (
 	timeout              *time.Duration
 	cpuListStr           *string
 	parallel             *int
+	shuffle              *string
 	testlog              *string
 
 	haveExamples bool // are there examples?
@@ -1456,6 +1459,25 @@ func (m *M) Run() (code int) {
 		return
 	}
 
+	if *shuffle != "off" {
+		var n int64
+		var err error
+		if *shuffle == "on" {
+			n = time.Now().UnixNano()
+		} else {
+			n, err = strconv.ParseInt(*shuffle, 10, 64)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, `testing: -shuffle should be "off", "on", or a valid integer:`, err)
+				m.exitCode = 2
+				return
+			}
+		}
+		fmt.Println("-test.shuffle", n)
+		rng := rand.New(rand.NewSource(n))
+		rng.Shuffle(len(m.tests), func(i, j int) { m.tests[i], m.tests[j] = m.tests[j], m.tests[i] })
+		rng.Shuffle(len(m.benchmarks), func(i, j int) { m.benchmarks[i], m.benchmarks[j] = m.benchmarks[j], m.benchmarks[i] })
+	}
+
 	parseCpuList()
 
 	m.before()