Add some more tests for MemPostings_Delete

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

tsdb/index/postings_test.go

@@ -973,6 +973,7 @@ func TestMemPostingsStats(t *testing.T) {
 }
 
 func TestMemPostings_Delete(t *testing.T) {
+	t.Run("some postings", func(t *testing.T) {
 		p := NewMemPostings()
 		p.Add(1, labels.FromStrings("lbl1", "a"))
 		p.Add(2, labels.FromStrings("lbl1", "b"))
@@ -1004,6 +1005,37 @@ func TestMemPostings_Delete(t *testing.T) {
 		expanded, err = ExpandPostings(deleted)
 		require.NoError(t, err)
 		require.Empty(t, expanded, "expected empty postings, got %v", expanded)
+	})
+
+	t.Run("all postings", func(t *testing.T) {
+		p := NewMemPostings()
+		p.Add(1, labels.FromStrings("lbl1", "a"))
+		p.Add(2, labels.FromStrings("lbl1", "b"))
+		p.Add(3, labels.FromStrings("lbl2", "a"))
+
+		deletedRefs := map[storage.SeriesRef]struct{}{1: {}, 2: {}, 3: {}}
+		affectedLabels := map[labels.Label]struct{}{
+			{Name: "lbl1", Value: "a"}: {},
+			{Name: "lbl1", Value: "b"}: {},
+			{Name: "lbl1", Value: "c"}: {},
+		}
+		p.Delete(deletedRefs, affectedLabels)
+		after := p.Get(allPostingsKey.Name, allPostingsKey.Value)
+		expanded, err := ExpandPostings(after)
+		require.NoError(t, err)
+		require.Empty(t, expanded)
+	})
+
+	t.Run("nothing on empty mempostings", func(t *testing.T) {
+		p := NewMemPostings()
+		deletedRefs := map[storage.SeriesRef]struct{}{}
+		affectedLabels := map[labels.Label]struct{}{}
+		p.Delete(deletedRefs, affectedLabels)
+		after := p.Get(allPostingsKey.Name, allPostingsKey.Value)
+		expanded, err := ExpandPostings(after)
+		require.NoError(t, err)
+		require.Empty(t, expanded)
+	})
 }
 
 // BenchmarkMemPostings_Delete is quite heavy, so consider running it with