fix: Check if injected CSS String is already in the list of injected styles (#12479)

* Check if injected CSS String is already in the list of injected styles

* Change to package for unit testing

* Unit test

* Add missing imports

1 files changed, 24 insertions, 0 deletions

diff --git a/server/src/test/java/com/vaadin/server/PageTest.java b/server/src/test/java/com/vaadin/server/PageTest.java
index adb9e93227..5ac4c5be14 100644
--- a/server/src/test/java/com/vaadin/server/PageTest.java
+++ b/server/src/test/java/com/vaadin/server/PageTest.java
@@ -1,7 +1,10 @@
 package com.vaadin.server;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 
+import java.io.Writer;
+
 import org.easymock.EasyMock;
 import org.junit.Test;
 
@@ -45,6 +48,27 @@ public class PageTest {
                 page.getState(false).hasResizeListeners);
     }
 
+    @Test
+    public void cssStringInjectedTwice() throws PaintException {
+        TestPage page = new TestPage(EasyMock.createMock(UI.class),
+                EasyMock.createMock(PageState.class));
+        JsonPaintTarget paintTarget = new JsonPaintTarget(
+                EasyMock.createMock(LegacyCommunicationManager.class),
+                EasyMock.createMock(Writer.class), true);
+
+        page.getStyles().add(".my-style { color: red; }");
+        assertEquals(page.getStyles().pendingInjections.size(), 1);
+        page.paintContent(paintTarget);
+        assertEquals(page.getStyles().pendingInjections.size(), 0);
+        assertEquals(page.getStyles().injectedStyles.size(), 1);
+
+        page.getStyles().add(".my-style { color: red; }");
+        assertEquals(page.getStyles().pendingInjections.size(), 0);
+        page.paintContent(paintTarget);
+        assertEquals(page.getStyles().pendingInjections.size(), 0);
+        assertEquals(page.getStyles().injectedStyles.size(), 1);
+    }
+
     private static class TestPage extends Page {
 
         public TestPage(UI uI, PageState state) {