testing: support -test.count

This makes running benchmarks repeatedly easier.

main.go

@@ -216,7 +216,7 @@ func Build(pkgName, outpath string, options *compileopts.Options) error {
 
 // Test runs the tests in the given package. Returns whether the test passed and
 // possibly an error if the test failed to run.
-func Test(pkgName string, stdout, stderr io.Writer, options *compileopts.Options, testCompileOnly, testVerbose, testShort bool, testRunRegexp string, testBenchRegexp string, testBenchTime string, testBenchMem bool, outpath string) (bool, error) {
+func Test(pkgName string, stdout, stderr io.Writer, options *compileopts.Options, testCompileOnly, testVerbose, testShort bool, testRunRegexp string, testCount int, testBenchRegexp string, testBenchTime string, testBenchMem bool, outpath string) (bool, error) {
 	options.TestConfig.CompileTestBinary = true
 	config, err := builder.NewConfig(options)
 	if err != nil {
@@ -243,6 +243,9 @@ func Test(pkgName string, stdout, stderr io.Writer, options *compileopts.Options
 	if testBenchMem {
 		flags = append(flags, "-test.benchmem")
 	}
+	if testCount != 1 {
+		flags = append(flags, "-test.count="+strconv.Itoa(testCount))
+	}
 
 	buf := bytes.Buffer{}
 	passed := false
@@ -1405,6 +1408,7 @@ func main() {
 		flag.StringVar(&outpath, "o", "", "output filename")
 	}
 	var testCompileOnlyFlag, testVerboseFlag, testShortFlag *bool
+	var testCount *int
 	var testBenchRegexp *string
 	var testBenchTime *string
 	var testRunRegexp *string
@@ -1414,6 +1418,7 @@ func main() {
 		testVerboseFlag = flag.Bool("v", false, "verbose: print additional output")
 		testShortFlag = flag.Bool("short", false, "short: run smaller test suite to save time")
 		testRunRegexp = flag.String("run", "", "run: regexp of tests to run")
+		testCount = flag.Int("count", 1, "count: number of times to run tests/benchmarks `count` times")
 		testBenchRegexp = flag.String("bench", "", "run: regexp of benchmarks to run")
 		testBenchTime = flag.String("benchtime", "", "run each benchmark for duration `d`")
 		testBenchMem = flag.Bool("benchmem", false, "show memory stats for benchmarks")
@@ -1659,7 +1664,7 @@ func main() {
 				defer close(buf.done)
 				stdout := (*testStdout)(buf)
 				stderr := (*testStderr)(buf)
-				passed, err := Test(pkgName, stdout, stderr, options, *testCompileOnlyFlag, *testVerboseFlag, *testShortFlag, *testRunRegexp, *testBenchRegexp, *testBenchTime, *testBenchMem, outpath)
+				passed, err := Test(pkgName, stdout, stderr, options, *testCompileOnlyFlag, *testVerboseFlag, *testShortFlag, *testRunRegexp, *testCount, *testBenchRegexp, *testBenchTime, *testBenchMem, outpath)
 				if err != nil {
 					printCompilerError(func(args ...interface{}) {
 						fmt.Fprintln(stderr, args...)

src/testing/benchmark.go

@@ -27,6 +27,7 @@ var (
 	matchBenchmarks *string
 	benchmarkMemory *bool
 	benchTime       = benchTimeFlag{d: 1 * time.Second} // changed during test of testing package
+	testCount       *int
 )
 
 type benchTimeFlag struct {
@@ -213,11 +214,14 @@ func (b *B) doBench() BenchmarkResult {
 // of benchmark iterations until the benchmark runs for the requested benchtime.
 // run1 must have been called on b.
 func (b *B) launch() {
+	runtime.GC()
 	// Run the benchmark for at least the specified amount of time.
 	if b.benchTime.n > 0 {
 		b.runN(b.benchTime.n)
 	} else {
 		d := b.benchTime.d
+		b.failed = false
+		b.duration = 0
 		for n := int64(1); !b.failed && b.duration < d && n < 1e9; {
 			last := n
 			// Predict required iterations.
@@ -394,6 +398,7 @@ func runBenchmarks(matchString func(pat, str string) (bool, error), benchmarks [
 func (b *B) processBench(ctx *benchContext) {
 	benchName := b.name
 
+	for i := 0; i < flagCount; i++ {
 		if ctx != nil {
 			fmt.Printf("%-*s\t", ctx.maxLen, benchName)
 		}
@@ -414,6 +419,7 @@ func (b *B) processBench(ctx *benchContext) {
 			fmt.Println(results)
 		}
 	}
+}
 
 // Run benchmarks f as a subbenchmark with the given name. It reports
 // true if the subbenchmark succeeded.

src/testing/testing.go

@@ -26,6 +26,7 @@ var (
 	flagVerbose   bool
 	flagShort     bool
 	flagRunRegexp string
+	flagCount     int
 )
 
 var initRan bool
@@ -40,6 +41,7 @@ func Init() {
 	flag.BoolVar(&flagVerbose, "test.v", false, "verbose: print additional output")
 	flag.BoolVar(&flagShort, "test.short", false, "short: run smaller test suite to save time")
 	flag.StringVar(&flagRunRegexp, "test.run", "", "run: regexp of tests to run")
+	flag.IntVar(&flagCount, "test.count", 1, "run each test or benchmark `count` times")
 
 	initBenchmarkFlags()
 }
@@ -485,12 +487,14 @@ func runTests(matchString func(pat, str string) (bool, error), tests []InternalT
 		context: ctx,
 	}
 
+	for i := 0; i < flagCount; i++ {
 		tRunner(t, func(t *T) {
 			for _, test := range tests {
 				t.Run(test.Name, test.F)
 				ok = ok && !t.Failed()
 			}
 		})
+	}
 
 	return t.ran, ok
 }