Fix ComboboxScrollableWindowTest to use assertion (#11014)

uitest/src/test/java/com/vaadin/tests/components/window/ComboboxScrollableWindowTest.java

@@ -2,8 +2,10 @@ package com.vaadin.tests.components.window;
 
 import static com.vaadin.tests.components.window.ComboboxScrollableWindow.COMBOBOX_ID;
 import static com.vaadin.tests.components.window.ComboboxScrollableWindow.WINDOW_ID;
+import static org.junit.Assert.assertEquals;
 
 import org.junit.Test;
+import org.openqa.selenium.Point;
 import org.openqa.selenium.WebElement;
 
 import com.vaadin.testbench.By;
@@ -29,11 +31,20 @@ public class ComboboxScrollableWindowTest extends MultiBrowserTest {
         TestBenchElementCommands scrollable = testBenchElement(
                 scrollableElement);
         scrollable.scroll(1000);
+
+        int beforeClick = getScrollTop(scrollableElement);
         ComboBoxElement comboBox = $(ComboBoxElement.class).id(COMBOBOX_ID);
+        Point location = comboBox.getLocation();
+
         comboBox.openPopup();
         waitForElementPresent(By.className("v-filterselect-suggestpopup"));
 
-        compareScreen("combobox-open");
+        assertEquals("Clicking should not cause scrolling", beforeClick,
+                getScrollTop(scrollableElement));
+        assertEquals("ComboBox should not move along x-axis", location.getX(),
+                comboBox.getLocation().getX());
+        assertEquals("ComboBox should not move along y-axis", location.getY(),
+                comboBox.getLocation().getY());
     }
 
 }