1 files changed, 72 insertions, 0 deletions
diff --git a/runtimeindex_test.go b/runtimeindex_test.go
new file mode 100644
index 0000000..ba16fd9
--- /dev/null
+++ b/runtimeindex_test.go
@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package oblast_test
+
+import (
+	"database/sql"
+	"testing"
+
+	"go.xyrillian.de/oblast"
+	"go.xyrillian.de/oblast/internal/testhelpers/assert"
+	"go.xyrillian.de/oblast/internal/testhelpers/mock"
+	"go.xyrillian.de/oblast/internal/testhelpers/must"
+)
+
+func TestRuntimeIndex(t *testing.T) {
+	ctx := t.Context()
+	md := mock.NewDriver()
+	db := sql.OpenDB(md)
+
+	type basicRecord struct {
+		ID   int64  `db:"id"`
+		Name string `db:"name"`
+	}
+	store := oblast.MustNewStore[basicRecord](
+		oblast.SqliteDialect(),
+		oblast.TableNameIs("basic_records"),
+		oblast.PrimaryKeyIs("id"),
+	)
+
+	commonSetup := func() {
+		md.ForQuery(`SELECT "id", "name" FROM "basic_records" WHERE id > 0`).
+			ExpectQueryWithArgs().
+			AndReturnColumns("id", "name").
+			WithRow(1, "foo").
+			WithRow(2, "bar").
+			WithRow(3, "baz")
+	}
+
+	t.Run("Index", func(t *testing.T) {
+		byName := oblast.NewRuntimeIndex(func(r basicRecord) string { return r.Name })
+
+		// test success path
+		commonSetup()
+		result := must.Return(byName.IndexFrom(store.SelectWhere(ctx, db, `id > 0`)))(t)
+		assert.DeepEqual(t, result, map[string]basicRecord{
+			"foo": {1, "foo"},
+			"bar": {2, "bar"},
+			"baz": {3, "baz"},
+		})
+
+		// test error path
+		_, err := byName.IndexFrom(store.SelectWhere(ctx, db, `id = 1`))
+		assert.ErrEqual(t, err, `during Query(): unexpected query: SELECT "id", "name" FROM "basic_records" WHERE id = 1`)
+	})
+
+	t.Run("Partition", func(t *testing.T) {
+		byFirstLetter := oblast.NewRuntimeIndex(func(r basicRecord) string { return r.Name[0:1] })
+
+		// test success path
+		commonSetup()
+		result := must.Return(byFirstLetter.PartitionFrom(store.SelectWhere(ctx, db, `id > 0`)))(t)
+		assert.DeepEqual(t, result, map[string][]basicRecord{
+			"f": {{1, "foo"}},
+			"b": {{2, "bar"}, {3, "baz"}},
+		})
+
+		// test error path
+		_, err := byFirstLetter.PartitionFrom(store.SelectWhere(ctx, db, `id = 1`))
+		assert.ErrEqual(t, err, `during Query(): unexpected query: SELECT "id", "name" FROM "basic_records" WHERE id = 1`)
+	})
+}