Add emulation of transaction retries to memory impl of RunInTransaction.

impl/memory/datastore.go

Index: impl/memory/datastore.go
diff --git a/impl/memory/datastore.go b/impl/memory/datastore.go
index 079c05dfde4b6fab38a79e3d8e40ecb4b4f9b6bd..d622e8199a0bf32f41937eb4f81a391e9037746a 100644
--- a/impl/memory/datastore.go
+++ b/impl/memory/datastore.go
@@ -24,7 +24,7 @@ func useRDS(c context.Context) context.Context {
 
 		ns := curGID(ic).namespace
 		if x, ok := dsd.(*dataStoreData); ok {
-			return &dsImpl{x, ns, ic}
+			return &dsImpl{x, ns, 0, ic}
 		}
 		return &txnDsImpl{dsd.(*txnDataStoreData), ns}
 	})
@@ -34,9 +34,10 @@ func useRDS(c context.Context) context.Context {
 
 // dsImpl exists solely to bind the current c to the datastore data.
 type dsImpl struct {
-	data *dataStoreData
-	ns   string
-	c    context.Context
+	data         *dataStoreData
+	ns           string
+	txnFakeRetry int
+	c            context.Context
 }
 
 var _ ds.RawInterface = (*dsImpl)(nil)
@@ -107,6 +108,10 @@ func (d *dsImpl) CatchupIndexes() {
 	d.data.catchupIndexes()
 }
 
+func (d *dsImpl) SetTransactionRetryCount(count int) {
+	d.txnFakeRetry = count
+}
+
 func (d *dsImpl) Testable() ds.Testable {
 	return d
 }