.*: complete test to improve test coverage radondb#713

[summary]
add more test to improve the codecov of queryz.go and delete_plan.go

[test case]
src/backend/queryz_test.go
src/planner/delete_plan_test.go

[patch codecov]
src/backend/queryz.go 96.3%
src/planner/delete_plan.go 95.9%

src/backend/queryz.go

@@ -77,7 +77,7 @@ func (a byStartTime) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 func (a byStartTime) Less(i, j int) bool { return a[i].Start.Before(a[j].Start) }
 
 // GetQueryzRows returns a list of QueryDetailzRow sorted by start time
-func (qz *Queryz) GetQueryzRows() []QueryDetailzRow {
+func (qz *Queryz) GetQueryzRows() byStartTime {
 	qz.mu.RLock()
 	rows := []QueryDetailzRow{}
 	for _, qd := range qz.queryDetails {

src/backend/queryz_test.go

@@ -65,5 +65,9 @@ func TestQueryz(t *testing.T) {
 		rows := qz.GetQueryzRows()
 		assert.Equal(t, querys[0], rows[0].Query)
 		assert.Equal(t, querys[1], rows[1].Query)
+		// Test byStartTime.Swap() funciton to improve test coverage.
+		rows.Swap(0, 1)
+		assert.Equal(t, querys[0], rows[1].Query)
+		assert.Equal(t, querys[1], rows[0].Query)
 	}
 }

src/planner/delete_plan_test.go

@@ -261,7 +261,8 @@ func TestDeleteUnsupportedPlan(t *testing.T) {
 }
 
 func TestDeleteErrorPlan(t *testing.T) {
-	query := "delete from A where id=1"
+	query1 := "delete from A where id=1"
+	query2 := "delete from B"
 
 	log := xlog.NewStdLog(xlog.Level(xlog.PANIC))
 	database := "sbtest"
@@ -274,12 +275,29 @@ func TestDeleteErrorPlan(t *testing.T) {
 	err = route.AddForTest(database, router.MockTableMConfig())
 	assert.Nil(t, err)
 	databaseNull := ""
-	node, err := sqlparser.Parse(query)
-	assert.Nil(t, err)
-	plan := NewDeletePlan(log, databaseNull, query, node.(*sqlparser.Delete), route)
 
 	// plan build
 	{
+		// test delete with no database.
+		node, err := sqlparser.Parse(query1)
+		assert.Nil(t, err)
+		plan := NewDeletePlan(log, databaseNull, query1, node.(*sqlparser.Delete), route)
+		planTree := NewPlanTree()
+		{
+			err := planTree.Add(plan)
+			assert.Nil(t, err)
+		}
+
+		{
+			err := planTree.Build()
+			assert.NotNil(t, err)
+		}
+	}
+	{
+		// test route table "B" not exist
+		node, err := sqlparser.Parse(query2)
+		assert.Nil(t, err)
+		plan := NewDeletePlan(log, database, query2, node.(*sqlparser.Delete), route)
 		planTree := NewPlanTree()
 		{
 			err := planTree.Add(plan)