Fix order-dependent and stale-data assertions in CompletionTest

The checkCompletionContent method had two issues:

1. Order-dependent assertions: After async computation finishes,
   proposals from different processors are merged via
   CompletableFuture.thenAccept(addAll), and the final ordering
   depends on thread scheduling. The test assumed a fixed order.

2. Stale virtual table data: The completion proposal Table uses
   SWT.VIRTUAL. When setProposals() calls clearAll(), items are
   marked as unmaterialized but Widget.data is NOT cleared. The
   SWT.SetData handler sets both text and data, but getData() does
   not trigger SetData -- only getText()/getImage() do. The wait
   condition only checked item 0's text (via isComputingInfoEntry),
   leaving item 1 with stale data from the previous render.

Fixes:
- Check both items' text in the wait condition to force virtual
  table materialization via SWT.SetData for both items
- Make proposal assertions order-independent

Fixes #3880

Author: vogella

tests/org.eclipse.ui.genericeditor.tests/src/org/eclipse/ui/genericeditor/tests/CompletionTest.java

@@ -207,17 +207,25 @@ private void checkCompletionContent(final Table completionProposalList) {
 		completionProposalList.setSelection(initialProposalItem);
 
 		LongRunningBarContentAssistProcessor.finish();
+		// Check both items' text (not just item 0) to force the virtual SWT Table
+		// to materialize both items via SWT.SetData. Table.clearAll() marks items
+		// as unmaterialized but does not clear Widget.data, so reading getData()
+		// without prior getText() would return stale data from the previous render.
 		waitForProposalRelatedCondition("Proposal list should contain two items", completionProposalList,
-				() -> !isComputingInfoEntry(completionProposalList.getItem(0))
-						&& completionProposalList.getItemCount() == 2,
+				() -> completionProposalList.getItemCount() == 2
+						&& !isComputingInfoEntry(completionProposalList.getItem(0))
+						&& !isComputingInfoEntry(completionProposalList.getItem(1)),
 				5_000);
-		final TableItem firstCompletionProposalItem = completionProposalList.getItem(0);
-		final TableItem secondCompletionProposalItem = completionProposalList.getItem(1);
-		String firstCompletionProposalText = ((ICompletionProposal) firstCompletionProposalItem.getData()).getDisplayString();
-		String secondCompletionProposalText = ((ICompletionProposal) secondCompletionProposalItem.getData()).getDisplayString();
-		assertThat("Unexpected first proposal item", BAR_CONTENT_ASSIST_PROPOSAL, endsWith(firstCompletionProposalText));
-		assertThat("Unexpected second proposal item", LONG_RUNNING_BAR_CONTENT_ASSIST_PROPOSAL,
-				endsWith(secondCompletionProposalText));
+		String firstText = ((ICompletionProposal) completionProposalList.getItem(0).getData()).getDisplayString();
+		String secondText = ((ICompletionProposal) completionProposalList.getItem(1).getData()).getDisplayString();
+		// Async completion processors may return results in any order, so verify
+		// both proposals are present without assuming a specific order
+		boolean barFirst = BAR_CONTENT_ASSIST_PROPOSAL.endsWith(firstText)
+				&& LONG_RUNNING_BAR_CONTENT_ASSIST_PROPOSAL.endsWith(secondText);
+		boolean longRunningFirst = LONG_RUNNING_BAR_CONTENT_ASSIST_PROPOSAL.endsWith(firstText)
+				&& BAR_CONTENT_ASSIST_PROPOSAL.endsWith(secondText);
+		assertTrue(barFirst || longRunningFirst,
+				"Expected both bar and long-running proposals but got: [" + firstText + ", " + secondText + "]");
 		String selectedProposalString = ((ICompletionProposal) completionProposalList.getSelection()[0].getData())
 				.getDisplayString();
 		assertEquals(initialProposalString, selectedProposalString,