chore: change waiting condition for the test (#704)

change while() condition in testListLogEntriesSample() code.
instead of waiting for first printed log entry it waits for the entry
with designated payload. test will timeout after minute or succeed.

Fixes #692

Author: minherz

samples/snippets/src/test/java/com/example/logging/LoggingIT.java

@@ -112,12 +112,14 @@ public void testListLogEntriesSample() throws Exception {
     logging.flush();
     bout.reset();
 
-    // Check for mocked STDOUT having data
+    // Check for mocked STDOUT for having STRING_PAYLOAD2 substring
     String[] args = new String[] {TEST_LOG};
-    while (bout.toString().isEmpty()) {
+    while (!bout.toString().contains(STRING_PAYLOAD2)) {
       ListLogEntries.main(args);
       Thread.sleep(5000);
     }
+    // although the following assertion is formal
+    // the line is left to emphasis the validation that is done by the test
     assertThat(bout.toString().contains(STRING_PAYLOAD2)).isTrue();
   }