diff --git a/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/TestUtils.java b/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/TestUtils.java
index fce8de3e..07038de4 100644
--- a/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/TestUtils.java
+++ b/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/TestUtils.java
@@ -26,12 +26,14 @@
 import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.NullProgressMonitor;
+import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.ServiceCaller;
 import org.eclipse.ui.IEditorPart;
 import org.eclipse.ui.IWorkbenchPage;
 import org.eclipse.ui.IWorkbenchWindow;
 import org.eclipse.ui.PartInitException;
 import org.eclipse.ui.PlatformUI;
+import org.eclipse.ui.WorkbenchException;
 import org.eclipse.ui.ide.IDE;
 import org.junit.jupiter.api.TestInfo;
 
@@ -83,6 +85,12 @@ public static IEditorPart openInEditor(IFile file) throws PartInitException {
 		return part;
 	}
 
+	public static IEditorPart openInEditorInNewWindow(URI uri, String editorID) throws PartInitException {
+		IEditorPart part = IDE.openEditor(getNewWorkbenchWindowPage(), uri, editorID, true);
+		part.setFocus();
+		return part;
+	}
+
 	public static boolean closeEditor(IEditorPart editor, boolean save) {
 		IWorkbenchWindow workbenchWindow = PlatformUI.getWorkbench().getActiveWorkbenchWindow();
 		IWorkbenchPage page = workbenchWindow.getActivePage();
@@ -100,4 +108,13 @@ private static IWorkbenchPage getWorkbenchPage() {
 		return PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();
 	}
 
+	private static IWorkbenchPage getNewWorkbenchWindowPage() {
+		try {
+			return PlatformUI.getWorkbench().openWorkbenchWindow(null).getActivePage();
+		} catch (WorkbenchException e) {
+			Platform.getLog(TestUtils.class).error(e.getMessage(), e);
+		}
+		return null;
+	}
+
 }
diff --git a/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/internal/server/CLanguageServerEnableCacheTest.java b/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/internal/server/CLanguageServerEnableCacheTest.java
new file mode 100644
index 00000000..7474048e
--- /dev/null
+++ b/bundles/org.eclipse.cdt.lsp.test/src/org/eclipse/cdt/lsp/test/internal/server/CLanguageServerEnableCacheTest.java
@@ -0,0 +1,106 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Contributors to the Eclipse Foundation.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *   See git history
+ *******************************************************************************/
+
+package org.eclipse.cdt.lsp.test.internal.server;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.eclipse.cdt.lsp.internal.server.CLanguageServerEnableCache;
+import org.eclipse.cdt.lsp.plugin.LspPlugin;
+import org.eclipse.cdt.lsp.test.TestUtils;
+import org.eclipse.core.resources.IProject;
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.ui.IEditorPart;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInfo;
+import org.junit.jupiter.api.io.TempDir;
+
+class CLanguageServerEnableCacheTest {
+	private static final String EXTERNAL_HEADER_HPP = "ExternalHeader.hpp";
+	private IProject project;
+	private File externalFile;
+	private IEditorPart editor;
+	private IEditorPart editor2;
+	private CLanguageServerEnableCache cache = CLanguageServerEnableCache.getInstance();
+
+	@TempDir
+	private static File TEMP_DIR;
+
+	@BeforeEach
+	public void setUp(TestInfo testInfo) throws CoreException, IOException {
+		project = TestUtils.createCProject(TestUtils.getName(testInfo));
+		externalFile = new File(TEMP_DIR, EXTERNAL_HEADER_HPP);
+		externalFile.createNewFile();
+	}
+
+	@AfterEach
+	public void cleanUp() throws CoreException {
+		TestUtils.deleteProject(project);
+		if (externalFile != null) {
+			externalFile.delete();
+		}
+		if (editor != null) {
+			TestUtils.closeEditor(editor, false);
+		}
+		if (editor2 != null) {
+			TestUtils.closeEditor(editor2, false);
+		}
+	}
+
+	@Test
+	public void testCacheRemovedAfterFileGetsClosed() throws CoreException, IOException {
+		// GIVEN is an opened file in the LSP based C/C++ editor:
+		var uri = externalFile.toURI();
+		editor = TestUtils.openInEditor(uri, LspPlugin.LSP_C_EDITOR_ID);
+		// WHEN accessing the cached enable value:
+		var cachedUri = cache.get(uri);
+		// THEN the cache for the given URI is present:
+		assertTrue(cachedUri != null);
+		// AND the cache returns TRUE for the given file URI:
+		assertTrue(cachedUri.booleanValue());
+		// WHEN when the file gets closed:
+		TestUtils.closeEditor(editor, false);
+		// THEN the cached URI has been removed:
+		assertNull(cache.get(uri));
+	}
+
+	@Test
+	public void testCacheNotRemovedUntilAllOpenedEditorsHasBeenClosed() throws CoreException, IOException {
+		// GIVEN two opened files in the LSP based C/C++ editor in two workbench windows:
+		var uri = externalFile.toURI();
+		editor = TestUtils.openInEditor(uri, LspPlugin.LSP_C_EDITOR_ID);
+		editor2 = TestUtils.openInEditorInNewWindow(uri, LspPlugin.LSP_C_EDITOR_ID);
+		// WHEN accessing the cached enable value:
+		var cachedUri = cache.get(uri);
+		// THEN the cache for the given URI is present:
+		assertTrue(cachedUri != null);
+		// AND the cache returns TRUE for the given file URI:
+		assertTrue(cachedUri.booleanValue());
+		// WHEN when the file gets closed in the first window:
+		TestUtils.closeEditor(editor, false);
+		// THEN the cached URI has NOT been removed:
+		assertNotNull(cache.get(uri));
+		assertTrue(cache.get(uri).booleanValue());
+		// WHEN the file gets closed in the second window:
+		TestUtils.closeEditor(editor2, false);
+		// THEN the cached URI has been removed:
+		assertNull(cache.get(uri));
+	}
+
+}