Add test for Components in Grid Header (#9696)

Closes #9694

uitest/src/main/java/com/vaadin/tests/components/grid/GridComponents.java

@@ -26,7 +26,9 @@ public class GridComponents extends AbstractTestUIWithLog {
     protected void setup(VaadinRequest request) {
         Grid<String> grid = new Grid<>();
         grid.addColumn(string -> new Label(string), new ComponentRenderer())
-                .setCaption("Label");
+                .setId("label").setCaption("Column 0");
+        grid.getDefaultHeaderRow().getCell("label")
+                .setComponent(new Label("Label"));
         grid.addComponentColumn(string -> {
             if (textFields.containsKey(string)) {
                 log("Reusing old text field for: " + string);

uitest/src/test/java/com/vaadin/tests/components/grid/GridComponentsTest.java

@@ -12,6 +12,7 @@ import com.vaadin.testbench.elements.ButtonElement;
 import com.vaadin.testbench.elements.GridElement;
 import com.vaadin.testbench.elements.GridElement.GridCellElement;
 import com.vaadin.testbench.elements.GridElement.GridRowElement;
+import com.vaadin.testbench.elements.LabelElement;
 import com.vaadin.testbench.elements.NotificationElement;
 import com.vaadin.tests.tb3.MultiBrowserTest;
 
@@ -108,11 +109,24 @@ public class GridComponentsTest extends MultiBrowserTest {
         IntStream.range(300, 310).forEach(this::assertNoButton);
     }
 
+    @Test(expected = AssertionError.class)
+    public void testRow31() {
+        openTestURL();
+        // There is a button on row 31. This should fail.
+        assertNoButton(31);
+    }
+
     @Test
     public void testHeaders() {
         openTestURL();
         GridElement grid = $(GridElement.class).first();
-        Assert.assertEquals("Label", grid.getHeaderCell(0, 0).getText());
+        GridCellElement headerCell = grid.getHeaderCell(0, 0);
+        Assert.assertTrue("First header should contain a Label",
+                headerCell.isElementPresent(LabelElement.class));
+        Assert.assertEquals("Label",
+                headerCell.$(LabelElement.class).first().getText());
+        Assert.assertFalse("Second header should not contain a component",
+                grid.getHeaderCell(0, 1).isElementPresent(LabelElement.class));
         Assert.assertEquals("Other Components",
                 grid.getHeaderCell(0, 1).getText());
     }