testing: hoisted chunks of code to prepare for Run method

testing.go:
- run method will evolve into the Run method.
- added level field in common

benchmark.go:
- benchContext will be central to distinguish handling of benchmarks
  between normal Run methods and ones called from within Benchmark
  function.
- expandCPU will evolve into the processing hook for Run methods
  called within normal processing.
- runBench will evolve into the Run method.

Change-Id: I1816f9985d5ba94deb0ad062302ea9aee0bb5338
Reviewed-on: https://go-review.googlesource.com/18894Reviewed-by: Russ Cox <rsc@golang.org>

src/testing/benchmark.go

@@ -46,6 +46,7 @@ type InternalBenchmark struct {
 // affecting benchmark results.
 type B struct {
 	common
+	context          *benchContext
 	N                int
 	previousN        int           // number of iterations in the previous run
 	previousDuration time.Duration // total duration of the previous run
@@ -299,6 +300,10 @@ func benchmarkName(name string, n int) string {
 	return name
 }
 
+type benchContext struct {
+	maxLen int // The largest recorded benchmark name.
+}
+
 // An internal function but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
@@ -334,46 +339,72 @@ func runBenchmarksInternal(matchString func(pat, str string) (bool, error), benc
 		}
 	}
 	ok := true
+	main := &B{
+		common: common{name: "Main"},
+		context: &benchContext{
+			maxLen: maxlen,
+		},
+	}
 	for _, Benchmark := range bs {
-		for _, procs := range cpuList {
-			runtime.GOMAXPROCS(procs)
-			b := &B{
-				common: common{
-					signal: make(chan bool),
-					name:   Benchmark.Name,
-				},
-				benchFunc: Benchmark.F,
-			}
-			benchName := benchmarkName(Benchmark.Name, procs)
-			fmt.Printf("%-*s\t", maxlen, benchName)
-			r := b.run()
-			if b.failed {
-				ok = false
-				// The output could be very long here, but probably isn't.
-				// We print it all, regardless, because we don't want to trim the reason
-				// the benchmark failed.
-				fmt.Printf("--- FAIL: %s\n%s", benchName, b.output)
-				continue
-			}
-			results := r.String()
-			if *benchmarkMemory || b.showAllocResult {
-				results += "\t" + r.MemString()
-			}
-			fmt.Println(results)
-			// Unlike with tests, we ignore the -chatty flag and always print output for
-			// benchmarks since the output generation time will skew the results.
-			if len(b.output) > 0 {
-				b.trimOutput()
-				fmt.Printf("--- BENCH: %s\n%s", benchName, b.output)
-			}
-			if p := runtime.GOMAXPROCS(-1); p != procs {
-				fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
-			}
+		ok = ok && expandCPU(main, Benchmark)
+	}
+	return ok
+}
+
+func expandCPU(parent *B, Benchmark InternalBenchmark) bool {
+	ok := true
+	for _, procs := range cpuList {
+		runtime.GOMAXPROCS(procs)
+		benchName := benchmarkName(Benchmark.Name, procs)
+		fmt.Printf("%-*s\t", parent.context.maxLen, benchName)
+		b := parent.runBench(Benchmark.Name, Benchmark.F)
+		r := b.result
+		if b.failed {
+			ok = false
+			// The output could be very long here, but probably isn't.
+			// We print it all, regardless, because we don't want to trim the reason
+			// the benchmark failed.
+			fmt.Printf("--- FAIL: %s\n%s", benchName, b.output)
+			continue
+		}
+		results := r.String()
+		if *benchmarkMemory || b.showAllocResult {
+			results += "\t" + r.MemString()
+		}
+		fmt.Println(results)
+		// Unlike with tests, we ignore the -chatty flag and always print output for
+		// benchmarks since the output generation time will skew the results.
+		if len(b.output) > 0 {
+			b.trimOutput()
+			fmt.Printf("--- BENCH: %s\n%s", benchName, b.output)
+		}
+		if p := runtime.GOMAXPROCS(-1); p != procs {
+			fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
 		}
 	}
 	return ok
 }
 
+// runBench benchmarks f as a subbenchmark with the given name. It reports
+// whether there were any failures.
+//
+// A subbenchmark is like any other benchmark. A benchmark that calls Run at
+// least once will not be measured itself and will only run for one iteration.
+func (b *B) runBench(name string, f func(b *B)) *B {
+	sub := &B{
+		common: common{
+			signal: make(chan bool),
+			name:   name,
+			parent: &b.common,
+			level:  b.level + 1,
+		},
+		benchFunc: f,
+		context:   b.context,
+	}
+	sub.run()
+	return sub
+}
+
 // trimOutput shortens the output from a benchmark, which can be very long.
 func (b *B) trimOutput() {
 	// The output is likely to appear multiple times because the benchmark

src/testing/testing.go

@@ -204,6 +204,7 @@ type common struct {
 	finished bool
 
 	parent   *common
+	level    int       // Nesting depth of test or benchmark.
 	name     string    // Name of test or benchmark.
 	start    time.Time // Time test or benchmark started
 	duration time.Duration
@@ -524,6 +525,37 @@ func tRunner(t *T, fn func(t *T)) {
 	t.finished = true
 }
 
+// run runs f as a subtest of t called name. It reports whether f succeeded.
+// Run will block until all its parallel subtests have completed.
+func (t *T) run(name string, f func(t *T)) bool {
+	testName := name
+	if t.level > 0 {
+		testName = t.name + "/" + name
+	}
+	t = &T{
+		common: common{
+			barrier: make(chan bool),
+			signal:  make(chan bool),
+			name:    testName,
+			parent:  &t.common,
+			level:   t.level + 1,
+		},
+		context: t.context,
+	}
+
+	if *chatty {
+		fmt.Printf("=== RUN   %s\n", t.name)
+	}
+	// Instead of reducing the running count of this test before calling the
+	// tRunner and increasing it afterwards, we rely on tRunner keeping the
+	// count correct. This ensures that a sequence of sequential tests runs
+	// without being preempted, even when their parent is a parallel test. This
+	// may especially reduce surprises if *parallel == 1.
+	go tRunner(t, f)
+	<-t.signal
+	return !t.failed
+}
+
 // testContext holds all fields that are common to all tests. This includes
 // synchronization primitives to run at most *parallel tests.
 type testContext struct {
@@ -660,11 +692,10 @@ func RunTests(matchString func(pat, str string) (bool, error), tests []InternalT
 			},
 			context: ctx,
 		}
-
 		tRunner(t, func(t *T) {
-			for i := 0; i < len(tests); i++ {
+			for _, test := range tests {
 				// TODO: a version of this will be the Run method.
-				matched, err := matchString(*match, tests[i].Name)
+				matched, err := matchString(*match, test.Name)
 				if err != nil {
 					fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.run: %s\n", err)
 					os.Exit(1)
@@ -672,27 +703,7 @@ func RunTests(matchString func(pat, str string) (bool, error), tests []InternalT
 				if !matched {
 					continue
 				}
-				testName := tests[i].Name
-				t := &T{
-					common: common{
-						barrier: make(chan bool),
-						signal:  make(chan bool),
-						name:    testName,
-						parent:  &t.common,
-					},
-					context: t.context,
-				}
-
-				if *chatty {
-					fmt.Printf("=== RUN   %s\n", t.name)
-				}
-				// Instead of reducing the running count of this test before calling the
-				// tRunner and increasing it afterwards, we rely on tRunner keeping the
-				// count correct. This ensures that a sequence of sequential tests runs
-				// without being preempted, even when their parent is a parallel test. This
-				// may especially reduce surprises if *parallel == 1.
-				go tRunner(t, tests[i].F)
-				<-t.signal
+				t.run(test.Name, test.F)
 			}
 			// Run catching the signal rather than the tRunner as a separate
 			// goroutine to avoid adding a goroutine during the sequential