X test that shows problem of SliceByRootRev where untracked blocks are not...

X test that shows problem of SliceByRootRev where untracked blocks are not added uniformly into whole history

=== RUN   TestΔFtailSliceXXX
2021/08/05 18:07:35 zodb: FIXME: open /tmp/TestΔFtailSliceXXX2265944622/001/1.fs: raw cache is not ready for invalidations -> NoCache forced
    δftail_test.go:689: slice (@at0,@at2]:
        have: [@at1·{0 1}S @at2·{1}S]
        want: [@at1·{0 1}S @at2·{0 1}S]

wcfs/internal/zdata/δftail_test.go

@@ -222,6 +222,9 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 
 	// load zfile via root['treegen/file']
 	txn, ctx := transaction.New(context.Background())
+	defer func() {
+		txn.Abort()
+	}()
 	zconn, err := t.DB.Open(ctx, &zodb.ConnOptions{At: t.Head().At, NoPool: true});  X(err)
 	xzroot, err := zconn.Get(ctx, 0);  X(err)
 	zroot := xzroot.(*zodb.Map)
@@ -601,6 +604,92 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 	}
 }
 
+// TestΔFtailXXX XXX.
+func TestΔFtailSliceXXX(t_ *testing.T) {
+	t := xbtreetest.NewT(t_)
+	X := exc.Raiseif
+
+	xat := map[zodb.Tid]string{}
+	at0 := t.Head().At
+	xat[at0] = "at0"
+	δFtail := NewΔFtail(at0, t.DB)
+
+	t1 := t.CommitTree("T/B0:a,1:b")
+	xat[t1.At] = "at1"
+	δF, err := δFtail.Update(t1.ΔZ);  X(err)
+	// XXX assert δF == ø
+	_ = δF
+
+
+	// load zfile via root['treegen/file']
+	// XXX dup
+	txn, ctx := transaction.New(context.Background())
+	defer func() {
+		txn.Abort()
+	}()
+	zconn, err := t.DB.Open(ctx, &zodb.ConnOptions{At: t.Head().At, NoPool: true});  X(err)
+	xzroot, err := zconn.Get(ctx, 0);  X(err)
+	zroot := xzroot.(*zodb.Map)
+	err = zroot.PActivate(ctx);  X(err)
+	zfile := zroot.Data["treegen/file"].(*ZBigFile)
+	zroot.PDeactivate()
+//	foid := zfile.POid()
+	err = zfile.PActivate(ctx);  X(err)
+//	blksize   := zfile.blksize
+	blktabOid := zfile.blktab.POid()
+	if blktabOid != t.Root() {
+		t.Fatalf("BUG: zfile.blktab (%s)  !=  treeroot (%s)", blktabOid, t.Root())
+	}
+	zfile.PDeactivate()
+
+	// XXX dup
+	xtrackBlk := func(blk int64) {
+		_, path, zblk, _, err := zfile.LoadBlk(ctx, blk);  X(err)
+		δFtail.Track(zfile, blk, path, zblk)
+	}
+
+	// δfstr/vδfstr converts δf/vδf to string taking xat into account
+	// XXX dup
+	δfstr := func(δf *ΔFile) string {
+		s := fmt.Sprintf("@%s·%s", xat[δf.Rev], δf.Blocks)
+		if δf.Epoch {
+			s += "E"
+		}
+		if δf.Size {
+			s += "S"
+		}
+		return s
+	}
+	vδfstr := func(vδf []*ΔFile) string {
+		var s []string
+		for _, δf := range vδf {
+			s = append(s, δfstr(δf))
+		}
+		return fmt.Sprintf("%s", s)
+	}
+
+	// XXX explain
+	xtrackBlk(1)
+
+	t2 := t.CommitTree("t0:a,1:c Da:aa,b:b,c:c") // 1 -b+c, δa
+	xat[t2.At] = "at2"
+	δF, err = δFtail.Update(t2.ΔZ);  X(err)
+
+
+	lo := at0
+	hi := t2.At
+	vδf := δFtail.SliceByFileRev(zfile, lo, hi)
+	_01 := setI64{}; _01.Add(0); _01.Add(1)
+	vδf_ok := []*ΔFile{
+		&ΔFile{Rev: t1.At, Blocks: _01, Size: true},
+		&ΔFile{Rev: t2.At, Blocks: _01, Size: true},
+	}
+
+	if !reflect.DeepEqual(vδf, vδf_ok) {
+		t.Errorf("slice (@%s,@%s]:\nhave: %v\nwant: %v", xat[lo], xat[hi], vδfstr(vδf), vδfstr(vδf_ok))
+	}
+}
+
 
 // dataTabTxt returns string representation of {} dataTab.
 func dataTabTxt(dataTab map[string]string) string {