test: use JDT constant for JUnit 6 kind

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: f7a1a4d1-b63f-438b-a255-54976b0f5a0b

Author: wenytang-ms

java-extension/com.microsoft.java.test.plugin.test/src/com/microsoft/java/test/plugin/searcher/JUnit6TestSearcherTest.java

@@ -23,6 +23,7 @@
 import org.eclipse.jdt.core.IJavaProject;
 import org.eclipse.jdt.core.IType;
 import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.jdt.internal.junit.launcher.TestKindRegistry;
 import org.junit.Test;
 
 import com.microsoft.java.test.plugin.AbstractProjectsManagerBasedTest;
@@ -47,6 +48,6 @@ public void testFindNonStaticNestedTestClass() throws Exception {
                 nestedType, new NullProgressMonitor());
         assertTrue(discoveredTypes.contains(nestedType));
         assertEquals(TestKind.JUnit6, searcher.getTestKind());
-        assertEquals("org.eclipse.jdt.junit.loader.junit6", searcher.getJdtTestKind());
+        assertEquals(TestKindRegistry.JUNIT6_TEST_KIND_ID, searcher.getJdtTestKind());
     }
 }