fix: Make ComboBoxTester.selectItem respect native filtering (#2003)

vaadin-testbench-unit-junit5/src/test/java/com/vaadin/flow/component/combobox/ComboBoxCustomFilteringTesterTest.java

@@ -0,0 +1,91 @@
+/**
+ * Copyright (C) 2000-2025 Vaadin Ltd
+ *
+ * This program is available under Vaadin Commercial License and Service Terms.
+ *
+ * See <https://vaadin.com/commercial-license-and-service-terms> for the full
+ * license.
+ */
+package com.vaadin.flow.component.combobox;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import com.vaadin.flow.router.RouteConfiguration;
+import com.vaadin.testbench.unit.UIUnitTest;
+import com.vaadin.testbench.unit.ViewPackages;
+
+@ViewPackages
+public class ComboBoxCustomFilteringTesterTest extends UIUnitTest {
+
+    ComboBoxCustomFilteringView view;
+
+    @BeforeEach
+    void init() {
+        RouteConfiguration.forApplicationScope()
+                .setAnnotatedRoute(ComboBoxCustomFilteringView.class);
+        view = navigate(ComboBoxCustomFilteringView.class);
+    }
+
+    @Test
+    void selectItem_withCustomFiltering_respectsNativeFilter() {
+        // Test that selectItem respects the custom filtering
+        // "John" should be selectable as it matches the first name
+        test(view.combo).selectItem("John");
+        Assertions.assertEquals(view.items.get(0),
+                test(view.combo).getSelected());
+
+        // Clear selection
+        test(view.combo).selectItem(null);
+        Assertions.assertNull(test(view.combo).getSelected());
+
+        // "Jane" should also be selectable
+        test(view.combo).selectItem("Jane");
+        Assertions.assertEquals(view.items.get(1),
+                test(view.combo).getSelected());
+    }
+
+    @Test
+    void setFilter_withCustomFiltering_filtersCorrectly() {
+        // Test filtering by last name (which is part of custom filter logic)
+        test(view.combo).setFilter("Smith");
+        List<String> suggestions = test(view.combo).getSuggestions();
+
+        // Should find John Smith even though we're filtering by last name
+        Assertions.assertEquals(1, suggestions.size());
+        Assertions.assertEquals("John", suggestions.get(0));
+
+        // Test filtering by "son" which should match "Johnson"
+        test(view.combo).setFilter("son");
+        suggestions = test(view.combo).getSuggestions();
+        Assertions.assertEquals(1, suggestions.size());
+        Assertions.assertEquals("Bob", suggestions.get(0));
+
+        // Test filtering by "o" which should match John, Doe (Jane), Johnson
+        // (Bob)
+        test(view.combo).setFilter("o");
+        suggestions = test(view.combo).getSuggestions();
+        Assertions.assertEquals(3, suggestions.size());
+    }
+
+    @Test
+    void selectItem_afterManualFilter_selectsCorrectly() {
+        // Manually set a filter
+        test(view.combo).setFilter("Jane");
+        List<String> suggestions = test(view.combo).getSuggestions();
+        Assertions.assertEquals(1, suggestions.size());
+
+        // Clear the filter
+        test(view.combo).setFilter("");
+
+        // Select an item using selectItem
+        test(view.combo).selectItem("Jane");
+
+        // Verify the item was selected correctly
+        Assertions.assertEquals(view.items.get(1),
+                test(view.combo).getSelected(), "Jane should be selected");
+    }
+}

vaadin-testbench-unit-junit5/src/test/java/com/vaadin/flow/component/combobox/ComboBoxCustomFilteringView.java

@@ -0,0 +1,71 @@
+/**
+ * Copyright (C) 2000-2025 Vaadin Ltd
+ *
+ * This program is available under Vaadin Commercial License and Service Terms.
+ *
+ * See <https://vaadin.com/commercial-license-and-service-terms> for the full
+ * license.
+ */
+package com.vaadin.flow.component.combobox;
+
+import java.util.Arrays;
+import java.util.List;
+
+import com.vaadin.flow.component.Component;
+import com.vaadin.flow.component.HasComponents;
+import com.vaadin.flow.component.Tag;
+import com.vaadin.flow.router.Route;
+
+@Tag("div")
+@Route(value = "combo-custom-filter", registerAtStartup = false)
+public class ComboBoxCustomFilteringView extends Component
+        implements HasComponents {
+
+    ComboBox<Person> combo;
+    List<Person> items = Arrays.asList(new Person("John", "Smith"),
+            new Person("Jane", "Doe"), new Person("Bob", "Johnson"));
+
+    public ComboBoxCustomFilteringView() {
+        combo = new ComboBox<>("Person Selector");
+
+        // Custom filter that matches both first and last name
+        combo.setItems((person, filterText) -> {
+            if (filterText == null || filterText.isEmpty()) {
+                return true;
+            }
+            String lowerFilter = filterText.toLowerCase();
+            // Custom logic: match if filter text is found in either first or
+            // last name
+            return person.getFirstName().toLowerCase().contains(lowerFilter)
+                    || person.getLastName().toLowerCase().contains(lowerFilter);
+        }, items);
+
+        // Display only the first name in the dropdown
+        combo.setItemLabelGenerator(person -> person.getFirstName());
+
+        add(combo);
+    }
+
+    public static class Person {
+        private String firstName;
+        private String lastName;
+
+        public Person(String firstName, String lastName) {
+            this.firstName = firstName;
+            this.lastName = lastName;
+        }
+
+        public String getFirstName() {
+            return firstName;
+        }
+
+        public String getLastName() {
+            return lastName;
+        }
+
+        @Override
+        public String toString() {
+            return firstName + " " + lastName;
+        }
+    }
+}

vaadin-testbench-unit-shared/src/main/java/com/vaadin/flow/component/combobox/ComboBoxTester.java

@@ -73,6 +73,9 @@ public void selectItem(String selection) {
             setValueAsUser(null);
             return;
         }
+        // Apply the filter to respect native filtering behavior
+        setFilter(selection);
+
         final List<Y> suggestionItems = getSuggestionItems();
         final ItemLabelGenerator<Y> itemLabelGenerator = getComponent()
                 .getItemLabelGenerator();
@@ -84,6 +87,9 @@ public void selectItem(String selection) {
                     "No item found for '" + selection + "'");
         }
         setValueAsUser(filtered.get(0));
+
+        // Clear the filter after selection
+        setFilter("");
     }
 
     /**

vaadin-testbench-unit-shared/src/main/java/com/vaadin/flow/component/combobox/MultiSelectComboBoxTester.java

@@ -76,17 +76,28 @@ public void selectItem(String... selection) {
             return;
         }
         List<String> toBeSelected = Arrays.asList(selection);
-        final List<Y> suggestionItems = getSuggestionItems();
-        final ItemLabelGenerator<Y> itemLabelGenerator = getComponent()
-                .getItemLabelGenerator();
-        final List<Y> filtered = suggestionItems.stream().filter(
-                item -> toBeSelected.contains(itemLabelGenerator.apply(item)))
-                .collect(Collectors.toList());
-        if (filtered.size() < 1) {
+
+        // Apply filter for each selection to respect native filtering behavior
+        // We need to collect all matching items from potentially different
+        // filter results
+        List<Y> allMatchingItems = toBeSelected.stream().flatMap(sel -> {
+            setFilter(sel);
+            final List<Y> suggestionItems = getSuggestionItems();
+            final ItemLabelGenerator<Y> itemLabelGenerator = getComponent()
+                    .getItemLabelGenerator();
+            return suggestionItems.stream()
+                    .filter(item -> sel.equals(itemLabelGenerator.apply(item)));
+        }).distinct().collect(Collectors.toList());
+
+        if (allMatchingItems.size() < 1) {
             throw new IllegalArgumentException(
-                    "No item found for '" + selection + "'");
+                    "No item found for '" + Arrays.toString(selection) + "'");
         }
-        getComponent().setValue(filtered);
+
+        // Clear the filter after selection
+        setFilter("");
+
+        getComponent().setValue(allMatchingItems);
     }
 
     /**