Add JUnit 6 dependency to getting-started.adoc (#4914)

* Add JUnit 6 dependency to getting-started.adoc

Added JUnit 6 dependency for Vaadin TestBench.

* more clarifications

---------

Co-authored-by: Manuel Carrasco Moñino <[email protected]>

Author: mshabarov

articles/flow/testing/end-to-end/getting-started.adoc

@@ -29,14 +29,20 @@ To start using TestBench in an existing project, you need to add the TestBench d
 ----
 [source,xml]
 ----
-<source-info group="JUnit 5 (Since Vaadin 24.0)"></source-info>
+<source-info group="JUnit 5/6 (Since Vaadin 24.0 and 25.0 respectively)"></source-info>
 <dependency>
     <groupId>com.vaadin</groupId>
-    <artifactId>vaadin-testbench-junit5</artifactId>
+    <artifactId>vaadin-testbench-junit6</artifactId> <!-- or vaadin-testbench-junit5 -->
     <scope>test</scope>
 </dependency>
 ----
 --
+
+[NOTE]
+====
+Starting with Vaadin 25 and Spring Boot 4, the default test framework is JUnit 6 (JUnit Platform). JUnit 6 maintains API compatibility with JUnit 5, so `vaadin-testbench-junit5` and `vaadin-testbench-junit6` work with both, but have transitive JUnit dependencies aligned with the respective versions.
+====
+
 The `test` scope and version number are predefined by the Vaadin BOM.
 
 To be able to run tests locally, you might need to install a WebDriver for your browser. See <<installing-webdrivers#,Installing WebDrivers>> for more details.

articles/flow/testing/ui-unit/getting-started.adoc

@@ -34,15 +34,15 @@ To start creating UI unit tests in an existing project, you need to add the Test
 <source-info group="JUnit 5/6"></source-info>
 <dependency>
     <groupId>com.vaadin</groupId>
-    <artifactId>vaadin-testbench-unit-junit5</artifactId>
+    <artifactId>vaadin-testbench-unit-junit6</artifactId> <!-- or vaadin-testbench-unit-junit5 -->
     <scope>test</scope>
 </dependency>
 ----
 --
 
 [NOTE]
 ====
-Starting with Vaadin 25 and Spring Boot 4, the default test framework is JUnit 6 (JUnit Platform). JUnit 6 maintains API compatibility with JUnit 5, so `vaadin-testbench-unit-junit5` works with both.
+Starting with Vaadin 25 and Spring Boot 4, the default test framework is JUnit 6 (JUnit Platform). JUnit 6 maintains API compatibility with JUnit 5, so `vaadin-testbench-unit-junit5` and `vaadin-testbench-unit-junit6` work with both, but have transitive JUnit dependencies aligned with the respective versions.
 
 For JUnit 4 tests using [classname]`UIUnit4Test`, the `junit-vintage-engine` dependency is required because JUnit 6 doesn't natively execute JUnit 4 tests. Without it, tests won't be detected or executed.