testing: prepare for the introduction of Run methods

The biggest change is that each test is now responsible for managing
the starting and stopping of its parallel subtests.

The "Main" test could be run as a tRunner as well. This shows that
the introduction of subtests is merely a generalization of and
consistent with the current semantics.

Change-Id: Ibf8388c08f85d4b2c0df69c069326762ed36a72e
Reviewed-on: https://go-review.googlesource.com/18893
Reviewed-by: Russ Cox <rsc@golang.org>

src/testing/sub_test.go

@@ -0,0 +1,101 @@
+// Copyright 2016 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 testing
+
+func TestTestContext(t *T) {
+	const (
+		add1 = 0
+		done = 1
+	)
+	// After each of the calls are applied to the context, the
+	type call struct {
+		typ int // run or done
+		// result from applying the call
+		running int
+		waiting int
+		started bool
+	}
+	testCases := []struct {
+		max int
+		run []call
+	}{{
+		max: 1,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: done, running: 0, waiting: 0, started: false},
+		},
+	}, {
+		max: 1,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: add1, running: 1, waiting: 1, started: false},
+			{typ: done, running: 1, waiting: 0, started: true},
+			{typ: done, running: 0, waiting: 0, started: false},
+			{typ: add1, running: 1, waiting: 0, started: true},
+		},
+	}, {
+		max: 3,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: add1, running: 2, waiting: 0, started: true},
+			{typ: add1, running: 3, waiting: 0, started: true},
+			{typ: add1, running: 3, waiting: 1, started: false},
+			{typ: add1, running: 3, waiting: 2, started: false},
+			{typ: add1, running: 3, waiting: 3, started: false},
+			{typ: done, running: 3, waiting: 2, started: true},
+			{typ: add1, running: 3, waiting: 3, started: false},
+			{typ: done, running: 3, waiting: 2, started: true},
+			{typ: done, running: 3, waiting: 1, started: true},
+			{typ: done, running: 3, waiting: 0, started: true},
+			{typ: done, running: 2, waiting: 0, started: false},
+			{typ: done, running: 1, waiting: 0, started: false},
+			{typ: done, running: 0, waiting: 0, started: false},
+		},
+	}}
+	for i, tc := range testCases {
+		ctx := &testContext{
+			startParallel: make(chan bool),
+			maxParallel:   tc.max,
+		}
+		for j, call := range tc.run {
+			doCall := func(f func()) chan bool {
+				done := make(chan bool)
+				go func() {
+					f()
+					done <- true
+				}()
+				return done
+			}
+			started := false
+			switch call.typ {
+			case add1:
+				signal := doCall(ctx.waitParallel)
+				select {
+				case <-signal:
+					started = true
+				case ctx.startParallel <- true:
+					<-signal
+				}
+			case done:
+				signal := doCall(ctx.release)
+				select {
+				case <-signal:
+				case <-ctx.startParallel:
+					started = true
+					<-signal
+				}
+			}
+			if started != call.started {
+				t.Errorf("%d:%d:started: got %v; want %v", i, j, started, call.started)
+			}
+			if ctx.running != call.running {
+				t.Errorf("%d:%d:running: got %v; want %v", i, j, ctx.running, call.running)
+			}
+			if ctx.numWaiting != call.waiting {
+				t.Errorf("%d:%d:waiting: got %v; want %v", i, j, ctx.numWaiting, call.waiting)
+			}
+		}
+	}
+}