Add a @timeout example for 'poll until' logic

Closes #1926

Author: rmannibucau

documentation/src/docs/asciidoc/user-guide/writing-tests.adoc

@@ -1695,6 +1695,25 @@ omitted. Specifying no unit is equivalent to using seconds.
 | `42 d`          | `@Timeout(value = 42, unit = DAYS)`
 |===
 
+==== Use @Timeout for polling tests
+
+It is common to write tests waiting for some updates.
+In some cases you can rewrite the logic to use a `CountDownLatch` or any other synchronization
+mechanism but sometimes it is not possible - generally when depending on an external system.
+These tests require some timeout to ensure they don't hang the test suite forever and
+the test fails if the waiting condition "never" happens.
+With `@Timeout` it becomes very easy to write such tests since the test itself just require
+to become an infinite loop:
+
+[source,java]
+----
+include::{testDir}/example/PollingTimeout.java[tags=user_guide,indent=0]
+----
+
+Such a simple usage enables to implement "test when" or "wait until" logic very easily.
+
+Alternatively, you can use a library handling for you the awaiting like the well-known
+link:https://github.com/awaitility/awaitility[Awaitility].
 
 [[writing-tests-parallel-execution]]
 === Parallel Execution

documentation/src/test/java/example/PollingTimeout.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2015-2019 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package example;
+
+import org.junit.jupiter.api.Timeout;
+
+class PollingTimeout {
+	// tag::user_guide[]
+	@Timeout(5) // 5s
+	void waitUntil() throws InterruptedException {
+		while (!isConditionTrue()) {
+			Thread.sleep(250); // use some adapted retry duration
+		}
+		// if needed asserts on the result of the awaited condition
+	}
+	// end::user_guide[]
+
+	private boolean isConditionTrue() {
+		return true;
+	}
+}