Add a new integration test framework

I have had this living in a separate branch for now, but we need this in the main branch sooner rather than later.

One big advantage of this is that integration tests can live in any package, not just hugolib.

lazy/init.go

@@ -16,6 +16,7 @@ package lazy
 import (
 	"context"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/pkg/errors"
@@ -28,6 +29,9 @@ func New() *Init {
 
 // Init holds a graph of lazily initialized dependencies.
 type Init struct {
+	// Used in tests
+	initCount uint64
+
 	mu sync.Mutex
 
 	prev     *Init
@@ -47,6 +51,12 @@ func (ini *Init) Add(initFn func() (interface{}, error)) *Init {
 	return ini.add(false, initFn)
 }
 
+// InitCount gets the number of this this Init has been initialized.
+func (ini *Init) InitCount() int {
+	i := atomic.LoadUint64(&ini.initCount)
+	return int(i)
+}
+
 // AddWithTimeout is same as Add, but with a timeout that aborts initialization.
 func (ini *Init) AddWithTimeout(timeout time.Duration, f func(ctx context.Context) (interface{}, error)) *Init {
 	return ini.Add(func() (interface{}, error) {
@@ -77,6 +87,7 @@ func (ini *Init) Do() (interface{}, error) {
 	}
 
 	ini.init.Do(func() {
+		atomic.AddUint64(&ini.initCount, 1)
 		prev := ini.prev
 		if prev != nil {
 			// A branch. Initialize the ancestors.