Fixed Stats method for Not iterator.

Added unit tests for Not iterator.

graph/iterator/not_iterator.go

@@ -154,15 +154,12 @@ func (it *Not) Optimize() (graph.Iterator, bool) {
 }
 
 func (it *Not) Stats() graph.IteratorStats {
-	subitStats := it.primaryIt.Stats()
-	// TODO(barakmich): These should really come from the triplestore itself
-	fanoutFactor := int64(20)
-	checkConstant := int64(1)
-	nextConstant := int64(2)
+	primaryStats := it.primaryIt.Stats()
+	allStats := it.allIt.Stats()
 	return graph.IteratorStats{
-		NextCost:     nextConstant + subitStats.NextCost,
-		ContainsCost: checkConstant + subitStats.ContainsCost,
-		Size:         fanoutFactor * subitStats.Size,
+		NextCost:     allStats.NextCost + primaryStats.ContainsCost,
+		ContainsCost: primaryStats.ContainsCost,
+		Size:         allStats.Size - primaryStats.Size,
 		Next:         it.runstats.Next,
 		Contains:     it.runstats.Contains,
 		ContainsNext: it.runstats.ContainsNext,

graph/iterator/not_iterator_test.go

@@ -0,0 +1,44 @@
+package iterator
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNotIteratorBasics(t *testing.T) {
+	allIt := newFixed()
+	allIt.Add(1)
+	allIt.Add(2)
+	allIt.Add(3)
+	allIt.Add(4)
+
+	toComplementIt := newFixed()
+	toComplementIt.Add(2)
+	toComplementIt.Add(4)
+
+	not := NewNot(toComplementIt, allIt)
+
+	if v, _ := not.Size(); v != 2 {
+		t.Errorf("Unexpected iterator size: got:%d, expected: %d", v, 2)
+	}
+
+	expect := []int{1, 3}
+	for i := 0; i < 2; i++ {
+		if got := iterated(not); !reflect.DeepEqual(got, expect) {
+			t.Errorf("Failed to iterate Not correctly on repeat %d: got:%v expected:%v", i, got, expect)
+		}
+		not.Reset()
+	}
+
+	for _, v := range []int{1, 3} {
+		if !not.Contains(v) {
+			t.Errorf("Failed to correctly check %d as true", v)
+		}
+	}
+
+	for _, v := range []int{2, 4} {
+		if not.Contains(v) {
+			t.Errorf("Failed to correctly check %d as false", v)
+		}
+	}
+}