Improve assertions in BrowserFunction registration test #3254

The test case
test_BrowserFunction_availableOnLoad_concurrentInstances_issue20
currently only asserts that the two involved progress listeners were
successfully executed. In case of a failure, there is not information
about which of the listeners was not executed. In addition, the
listeners may even fail to execute with an exception, but that exception
is currently swallowed.

With this change, exceptions are properly propagated to test failures
and in case a listener is not executed at all, the error message will
report for which of them that is the case.

Contributes to
#3254

Author: HeikoKlare

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

@@ -3002,11 +3002,14 @@ public void test_BrowserFunction_availableOnLoad_concurrentInstances_issue20() {
 		@Override
 		public Object function(Object[] arguments) { return null; }
 	};
+	AtomicReference<SWTException> exceptionInBrowser1 = new AtomicReference<>();
 	b1.addProgressListener(completedAdapter(e -> {
 		try {
 			b1.evaluate("options();");
 			browser1FuncAvailable.set(true);
-		} catch (SWTException ignored) {}
+		} catch (SWTException ex) {
+			exceptionInBrowser1.set(ex);
+		}
 	}));
 	createdBroswers.add(b1);
 
@@ -3017,19 +3020,29 @@ public void test_BrowserFunction_availableOnLoad_concurrentInstances_issue20() {
 		@Override
 		public Object function(Object[] arguments) { return null; }
 	};
+	AtomicReference<SWTException> exceptionInBrowser2 = new AtomicReference<>();
 	b2.addProgressListener(completedAdapter(e -> {
 		try {
 			b2.evaluate("options();");
 			browser2FuncAvailable.set(true);
-		} catch (SWTException ignored) {}
+		} catch (SWTException ex) {
+			exceptionInBrowser2.set(ex);
+		}
 	}));
 	createdBroswers.add(b2);
 
 	shell.open();
-	assertTrue(
-		waitForPassCondition(() -> browser1FuncAvailable.get() && browser2FuncAvailable.get()),
-		"BrowserFunction must be available when page load completes on both browsers "
-		+ "(regression of https://github.com/eclipse-platform/eclipse.platform.swt/issues/20)");
+	waitForPassCondition(() -> (exceptionInBrowser1.get() != null || browser1FuncAvailable.get())
+			&& (exceptionInBrowser2.get() != null || browser2FuncAvailable.get()));
+
+	if (exceptionInBrowser1.get() != null) {
+		throw exceptionInBrowser1.get();
+	}
+	if (exceptionInBrowser2.get() != null) {
+		throw exceptionInBrowser2.get();
+	}
+	assertTrue(browser1FuncAvailable.get(), "BrowserFunction for first browser missing when page load completed");
+	assertTrue(browser2FuncAvailable.get(), "BrowserFunction for second browser missing when page load completed");
 }
 
 @Test