tstest: rename from testy.

Signed-off-by: David Anderson <danderson@tailscale.com>

tstest/resource.go

@@ -0,0 +1,72 @@
+// Copyright (c) 2020 Tailscale Inc & 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 tstest
+
+import (
+	"bytes"
+	"runtime"
+	"runtime/pprof"
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type ResourceCheck struct {
+	startNumRoutines int
+	startDump        string
+}
+
+func NewResourceCheck() *ResourceCheck {
+	// NOTE(apenwarr): I'd rather not pre-generate a goroutine dump here.
+	//  However, it turns out to be tricky to debug when eg. the initial
+	//  goroutine count > the ending goroutine count, because of course
+	//  the missing ones are not in the final dump. Also, we have to
+	//  render the profile as a string right away, because the
+	//  pprof.Profile object doesn't stay stable over time. Every time
+	//  you render the string, you might get a different answer.
+	r := &ResourceCheck{}
+	r.startNumRoutines, r.startDump = goroutineDump()
+	return r
+}
+
+func goroutineDump() (int, string) {
+	p := pprof.Lookup("goroutine")
+	b := &bytes.Buffer{}
+	p.WriteTo(b, 1)
+	return p.Count(), b.String()
+}
+
+func (r *ResourceCheck) Assert(t *testing.T) {
+	t.Helper()
+	want := r.startNumRoutines
+
+	// Some goroutines might be still exiting, so give them a chance
+	got := runtime.NumGoroutine()
+	if want != got {
+		_, dump := goroutineDump()
+		for i := 0; i < 100; i++ {
+			got = runtime.NumGoroutine()
+			if want == got {
+				break
+			}
+			time.Sleep(1 * time.Millisecond)
+		}
+
+		// If the count is *still* wrong, that's a failure.
+		if want != got {
+			t.Logf("goroutine diff:\n%v\n", cmp.Diff(r.startDump, dump))
+			t.Logf("goroutine count: expected %d, got %d\n", want, got)
+			// Don't fail if there are *fewer* goroutines than
+			// expected. That just might be some leftover ones
+			// from the previous test, which are pretty hard to
+			// eliminate.
+			if want < got {
+				t.Fatalf("goroutine count: expected %d, got %d\n", want, got)
+			}
+		}
+	}
+	t.Logf("Assert: goroutines before=%d after=%d - ok\n", got, want)
+}