Display the caption of the Empty selection in NativeSelect (#11191)

* Fixes #10937

- Previously if selected value is null, then index is set to -1; in current implementation if value is null and emptySelection is allowed then set the index to 0. (The position for the empty selection)

- Also, if changing the allowEmptySelection on the fly, ensure, that either index is to-reset to -1 by setting the selected value to null on the client-side (the value before was null) or preserve the value(value was different than empty).

* Change the test case

Since in this pr the behaviour of the NS is changed, therefore old test need to be adjusted.

Change: setting null as value will select empty selection. Before that nothing would be selected and value will be cleared.

Behaviour change in PR: Allow selecting null as value

3 files changed, 98 insertions, 0 deletions

diff --git a/uitest/src/main/java/com/vaadin/tests/components/abstractsingleselect/AbstractSingleSelection.java b/uitest/src/main/java/com/vaadin/tests/components/abstractsingleselect/AbstractSingleSelection.java
index fc10d13b53..44ea73dc88 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/abstractsingleselect/AbstractSingleSelection.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/abstractsingleselect/AbstractSingleSelection.java
@@ -50,6 +50,9 @@ public class AbstractSingleSelection extends AbstractTestUI {
                     .newInstance();
             select.setItems("Foo", "Bar", "Baz", "Reset");
             select.setSelectedItem("Bar");
+            if (select instanceof NativeSelect) {
+                ((NativeSelect) select).setEmptySelectionAllowed(false);
+            }
 
             select.addValueChangeListener(event -> {
                 if ("Reset".equals(event.getValue())) {
diff --git a/uitest/src/main/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNull.java b/uitest/src/main/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNull.java
new file mode 100644
index 0000000000..fc6c0f2f6c
--- /dev/null
+++ b/uitest/src/main/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNull.java
@@ -0,0 +1,36 @@
+package com.vaadin.tests.components.nativeselect;
+
+import com.vaadin.server.VaadinRequest;
+import com.vaadin.tests.components.AbstractTestUI;
+import com.vaadin.ui.NativeSelect;
+import com.vaadin.ui.Button;
+
+public class NativeSelectSetNull extends AbstractTestUI {
+    public static String EMPTY_SELECTION_TEXT = "Empty Selection";
+
+    @Override
+    protected void setup(VaadinRequest request) {
+        NativeSelect<Integer> select = new NativeSelect<>("Native Selection");
+
+        // Add some items
+        select.setItems(1, 2, 3, 45, 6);
+        select.setEmptySelectionAllowed(true);
+        select.setEmptySelectionCaption(EMPTY_SELECTION_TEXT);
+
+        Button changeSelect = new Button("Set value to 3",
+                e -> select.setValue(3));
+        changeSelect.setId("changeSelect");
+        Button setNull = new Button("Set value to null",
+                e -> select.setValue(null));
+        setNull.setId("setNull");
+        Button clear = new Button("Clear", e -> select.clear());
+        clear.setId("clear");
+
+        Button disable = new Button("Disable", e -> select
+                .setEmptySelectionAllowed(!select.isEmptySelectionAllowed()));
+        disable.setId("disable");
+
+        addComponent(select);
+        addComponents(changeSelect, setNull, clear, disable);
+    }
+}
diff --git a/uitest/src/test/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNullTest.java b/uitest/src/test/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNullTest.java
new file mode 100644
index 0000000000..90afe9f463
--- /dev/null
+++ b/uitest/src/test/java/com/vaadin/tests/components/nativeselect/NativeSelectSetNullTest.java
@@ -0,0 +1,59 @@
+package com.vaadin.tests.components.nativeselect;
+
+import com.vaadin.testbench.elements.NativeSelectElement;
+import com.vaadin.tests.tb3.MultiBrowserTest;
+import org.junit.Before;
+import org.junit.Test;
+import org.openqa.selenium.By;
+import org.openqa.selenium.WebElement;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class NativeSelectSetNullTest extends MultiBrowserTest {
+
+    @Before
+    public void setUp() {
+        openTestURL();
+    }
+
+    @Test
+    public void testCaptionSelected() {
+        getButtonOnId("setNull");
+        assertEquals(NativeSelectSetNull.EMPTY_SELECTION_TEXT,
+                getSelect().getValue());
+    }
+
+    @Test
+    public void changeSelectedValue() {
+        getButtonOnId("changeSelect").click();
+        assertEquals(3, Integer.valueOf(getSelect().getValue()).intValue());
+    }
+
+    @Test
+    public void clearSelection() {
+        getButtonOnId("clear").click();
+        assertEquals(NativeSelectSetNull.EMPTY_SELECTION_TEXT,
+                getSelect().getValue());
+    }
+
+    @Test
+    public void valuePreservedAfterAllowEmptySelectionChanged() {
+        getSelect().setValue("2");
+        getButtonOnId("disable").click();
+        assertEquals(2, Integer.valueOf(getSelect().getValue()).intValue());
+
+        getButtonOnId("disable").click();
+        getButtonOnId("setNull").click();
+        assertEquals(NativeSelectSetNull.EMPTY_SELECTION_TEXT,
+                getSelect().getValue());
+
+    }
+
+    protected NativeSelectElement getSelect() {
+        return $(NativeSelectElement.class).first();
+    }
+
+    protected WebElement getButtonOnId(String id) {
+        return findElement(By.id(id));
+    }
+}