add unit test for rowHashMap.

executor/hash_table.go

@@ -161,7 +161,10 @@ type entryStore struct {
 func (es *entryStore) init() {
 	es.slices = [][]entry{make([]entry, 0, initialEntrySliceLen)}
 	// Reserve the first empty entry, so entryAddr{} can represent nullEntryAddr.
-	es.put(entry{})
+	reserved := es.put(entry{})
+	if reserved != nullEntryAddr {
+		panic("entryStore: first entry is not nullEntryAddr")
+	}
 }
 
 func (es *entryStore) put(e entry) entryAddr {

executor/hash_table_test.go

@@ -0,0 +1,37 @@
+package executor
+
+import (
+	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/util/chunk"
+)
+
+func (s *pkgTestSuite) TestRowHashMap(c *C) {
+	m := newRowHashMap()
+	m.Put(1, chunk.RowPtr{ChkIdx: 1, RowIdx: 1})
+	c.Check(m.Get(1), DeepEquals, []chunk.RowPtr{{1, 1}})
+
+	rawData := map[uint64][]chunk.RowPtr{}
+	for i := uint64(0); i < 10; i++ {
+		for j := uint64(0); j < initialEntrySliceLen*i; j++ {
+			rawData[i] = append(rawData[i], chunk.RowPtr{ChkIdx: uint32(i), RowIdx: uint32(j)})
+		}
+	}
+	m = newRowHashMap()
+	// put all rawData into m vertically
+	for j := uint64(0); j < initialEntrySliceLen*9; j++ {
+		for i := 9; i >= 0; i-- {
+			i := uint64(i)
+			if !(j < initialEntrySliceLen*i) {
+				break
+			}
+			m.Put(i, rawData[i][j])
+		}
+	}
+	// check
+	totalCount := 0
+	for i := uint64(0); i < 10; i++ {
+		totalCount += len(rawData[i])
+		c.Check(m.Get(i), DeepEquals, rawData[i])
+	}
+	c.Check(m.Len(), Equals, totalCount)
+}