Add a simple test for Filter iterator

Add a simple unit test to validate the Filter iterator semantic.

Signed-off-by: Fabio Falzoi <[email protected]>

iterator_test.go

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Cilium
+
+package statedb
+
+import (
+	"testing"
+
+	"github.com/cilium/statedb/index"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFilter(t *testing.T) {
+	type testObject struct {
+		ID int
+	}
+
+	db, _ := NewDB(nil, NewExpVarMetrics(false))
+	idIndex := Index[*testObject, int]{
+		Name: "id",
+		FromObject: func(t *testObject) index.KeySet {
+			return index.NewKeySet(index.Int(t.ID))
+		},
+		FromKey: index.Int,
+		Unique:  true,
+	}
+	table, _ := NewTable("test", idIndex)
+	require.NoError(t, db.RegisterTable(table))
+
+	txn := db.WriteTxn(table)
+	table.Insert(txn, &testObject{ID: 1})
+	table.Insert(txn, &testObject{ID: 2})
+	table.Insert(txn, &testObject{ID: 3})
+	table.Insert(txn, &testObject{ID: 4})
+	table.Insert(txn, &testObject{ID: 5})
+	txn.Commit()
+
+	iter, _ := table.All(db.ReadTxn())
+	filtered := CollectSet(
+		Map(
+			Filter(
+				iter,
+				func(obj *testObject) bool {
+					return obj.ID%2 == 0
+				},
+			),
+			func(obj *testObject) int {
+				return obj.ID
+			},
+		),
+	)
+	assert.Len(t, filtered, 2)
+	assert.True(t, filtered.Has(2))
+	assert.True(t, filtered.Has(4))
+}