testing: add -test.count flag to run tests and benchmarks multiple times

The flag is available from the go test command as -count:

% go test -run XXX -bench . -count 3
PASS
BenchmarkSprintfEmpty      	30000000	        54.0 ns/op
BenchmarkSprintfEmpty      	30000000	        51.9 ns/op
BenchmarkSprintfEmpty      	30000000	        53.8 ns/op
BenchmarkSprintfString     	10000000	       238 ns/op
BenchmarkSprintfString     	10000000	       239 ns/op
BenchmarkSprintfString     	10000000	       234 ns/op
BenchmarkSprintfInt        	10000000	       232 ns/op
BenchmarkSprintfInt        	10000000	       226 ns/op
BenchmarkSprintfInt        	10000000	       225 ns/op
...

If -cpu is set, each test is run n times for each cpu value.

Original by r (CL 10663).

Change-Id: If3dfbdf21698952daac9249b5dbca66f5301e91b
Reviewed-on: https://go-review.googlesource.com/10669
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/go/alldocs.go

@@ -1135,6 +1135,11 @@ control the execution of any test:
 	    if -test.blockprofile is set without this flag, all blocking events
 	    are recorded, equivalent to -test.blockprofilerate=1.
 
+	-count n
+	    Run each test and benchmark n times (default 1).
+	    If -cpu is set, run n times for each GOMAXPROCS value.
+	    Examples are always run once.
+
 	-cover
 	    Enable coverage analysis.
 

src/cmd/go/test.go

@@ -141,6 +141,11 @@ control the execution of any test:
 	    if -test.blockprofile is set without this flag, all blocking events
 	    are recorded, equivalent to -test.blockprofilerate=1.
 
+	-count n
+	    Run each test and benchmark n times (default 1).
+	    If -cpu is set, run n times for each GOMAXPROCS value.
+	    Examples are always run once.
+
 	-cover
 	    Enable coverage analysis.
 

src/cmd/go/testflag.go

@@ -55,6 +55,7 @@ var testFlagDefn = []*testFlagSpec{
 	{name: "bench", passToTest: true},
 	{name: "benchmem", boolVar: new(bool), passToTest: true},
 	{name: "benchtime", passToTest: true},
+	{name: "count", passToTest: true},
 	{name: "coverprofile", passToTest: true},
 	{name: "cpu", passToTest: true},
 	{name: "cpuprofile", passToTest: true},

src/testing/testing.go

@@ -172,6 +172,7 @@ var (
 
 	// Report as tests are run; default is silent for success.
 	chatty           = flag.Bool("test.v", false, "verbose: print additional output")
+	count            = flag.Uint("test.count", 1, "run tests and benchmarks `n` times")
 	coverProfile     = flag.String("test.coverprofile", "", "write a coverage profile to the named file after execution")
 	match            = flag.String("test.run", "", "regular expression to select tests and examples to run")
 	memProfile       = flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
@@ -724,9 +725,13 @@ func parseCpuList() {
 			fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
 			os.Exit(1)
 		}
+		for i := uint(0); i < *count; i++ {
 			cpuList = append(cpuList, cpu)
 		}
+	}
 	if cpuList == nil {
+		for i := uint(0); i < *count; i++ {
 			cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
 		}
 	}
+}