Add diagnostics to failing Clipboard test and skip on non-GTK

This records additional information about the state of the remote process.
This will only hard fail on Linux as we have seen test pass on Linux,
and Linux is the primary target as the Clipboard is under development
on Linux only now for GTK4 work.

Part of #2553

Author: jonahgraham

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_dnd_Clipboard.java

@@ -15,13 +15,15 @@
 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 static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
 import java.lang.ProcessBuilder.Redirect;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.rmi.NotBoundException;
+import java.rmi.RemoteException;
 import java.rmi.registry.LocateRegistry;
 import java.rmi.registry.Registry;
 import java.util.List;
@@ -51,6 +53,7 @@
  */
 public class Test_org_eclipse_swt_dnd_Clipboard {
 
+	private static final int DEFAULT_TIMEOUT_MS = 10000;
 	@TempDir
 	static Path tempFolder;
 	static int uniqueId = 1;
@@ -168,16 +171,40 @@ private void startRemoteClipboardCommands() throws Exception {
 			throw new RuntimeException("Failed to get port");
 		});
 		assertNotEquals(0, port);
-		Registry reg = LocateRegistry.getRegistry("127.0.0.1", port);
-		long stopTime = System.currentTimeMillis() + 10000;
-		do {
+		try {
+			Registry reg = LocateRegistry.getRegistry("127.0.0.1", port);
+			long stopTime = System.currentTimeMillis() + DEFAULT_TIMEOUT_MS;
+			do {
+				try {
+					remote = (ClipboardCommands) reg.lookup(ClipboardCommands.ID);
+					break;
+				} catch (NotBoundException e) {
+					// try again because the remote app probably hasn't bound yet
+				}
+			} while (System.currentTimeMillis() < stopTime);
+		} catch (RemoteException e) {
+
+			Integer exitValue = null;
+			boolean waitFor = false;
 			try {
-				remote = (ClipboardCommands) reg.lookup(ClipboardCommands.ID);
-				break;
-			} catch (NotBoundException e) {
-				// try again because the remote app probably hasn't bound yet
+				waitFor = remoteClipboardProcess.waitFor(5, TimeUnit.SECONDS);
+				if (waitFor) {
+					exitValue = remoteClipboardProcess.exitValue();
+				}
+			} catch (InterruptedException e1) {
+				Thread.interrupted();
 			}
-		} while (System.currentTimeMillis() < stopTime);
+
+			String message = "Failed to get remote clipboards command, this seems to happen on macOS on I-build tests. Exception: "
+					+ e.toString() + " waitFor: " + waitFor + " exitValue: " + exitValue;
+
+			// Give some diagnostic information to help track down why this fails on build
+			// machine. We only hard error on Linux, for other platforms we allow test to
+			// just be skipped until we track down what is causing
+			// https://github.com/eclipse-platform/eclipse.platform.swt/issues/2553
+			assumeTrue(SwtTestUtil.isGTK, message);
+			throw new RuntimeException(message, e);
+		}
 		assertNotNull(remote);
 
 		// Run a no-op on the Swing event loop so that we know it is idle
@@ -318,7 +345,7 @@ public interface ExceptionalSupplier<T> {
 	 * the thread completes, or until a timeout is reached.
 	 */
 	private <T> T runOperationInThread(ExceptionalSupplier<T> supplier) throws RuntimeException {
-		return runOperationInThread(2000, supplier);
+		return runOperationInThread(DEFAULT_TIMEOUT_MS, supplier);
 	}
 
 	/**