Interface update, per-method Contexts.

filter/txnBuf/ds_txn.go

Index: filter/txnBuf/ds_txn.go
diff --git a/filter/txnBuf/ds_txn.go b/filter/txnBuf/ds_txn.go
index 7b25c607d2d4fc2a003d0a2ab8679d94be086929..35101a5cb967f0a82c4ad503494f04ecf50bebdd 100644
--- a/filter/txnBuf/ds_txn.go
+++ b/filter/txnBuf/ds_txn.go
@@ -116,6 +116,12 @@ func (d *dsTxnBuf) RunInTransaction(cb func(context.Context) error, opts *ds.Tra
 	return withTxnBuf(d.ic, cb, opts)
 }
 
-func (d *dsTxnBuf) Testable() ds.Testable {
-	return d.state.parentDS.Testable()
+func (d *dsTxnBuf) CurrentTransaction() ds.Transaction { return d.state.parentDS.CurrentTransaction() }

[dnj, 2016/09/01 15:25:39]

Perhaps in the future, we can synthesize transaction objects for the nested
transactions here. ATM we're just returning the underlying DS's transaction. I
was torn between implementing this right now and waiting until stronger support
for "WithTransaction" is implemented to do this, since it's not very useful
without that. 

[iannucci, 2016/09/16 01:01:13]

hm good point. Yes I think waiting on this is a good call, but please document
it in the mean time (in doc.go)

[dnj, 2016/09/16 05:44:42]

Done.

+
+func (d *dsTxnBuf) WithTransaction(t ds.Transaction) context.Context {
+	return d.state.parentDS.WithTransaction(nil)

[iannucci, 2016/09/16 01:01:13]

doesn't this need to remove transaction stuff from the context.Context as well?
Basically what the GetNoTxn function used to do?

[dnj, 2016/09/16 05:44:42]

Done.

+}
+
+func (d *dsTxnBuf) GetTestable() ds.Testable {
+	return nil

[dnj, 2016/09/01 15:25:39]

oops, I'll make sure this returns parentDS's Testable in next patch set, don't
know how this got nil'd.

[dnj, 2016/09/16 05:44:42]

Done.

 }