[FLINK-8070][yarn][tests] Print errors found in log files

This closes apache#5012.

flink-yarn-tests/src/test/java/org/apache/flink/yarn/YarnTestBase.java

@@ -69,6 +69,7 @@
 import java.io.IOException;
 import java.io.PrintStream;
 import java.io.PrintWriter;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
@@ -307,6 +308,7 @@ public static void ensureNoProhibitedStringInLogFiles(final String[] prohibited,
  Assert.assertTrue("Expecting directory " + cwd.getAbsolutePath() + " to exist", cwd.exists());
  Assert.assertTrue("Expecting directory " + cwd.getAbsolutePath() + " to be a directory", cwd.isDirectory());
 
+ List<String> prohibitedExcerpts = new ArrayList<>();
  File foundFile = findFile(cwd.getAbsolutePath(), new FilenameFilter() {
  @Override
  public boolean accept(File dir, String name) {
@@ -331,6 +333,24 @@ public boolean accept(File dir, String name) {
  // logging in FATAL to see the actual message in TRAVIS tests.
  Marker fatal = MarkerFactory.getMarker("FATAL");
  LOG.error(fatal, "Prohibited String '{}' in line '{}'", aProhibited, lineFromFile);
+
+ StringBuilder logExcerpt = new StringBuilder();
+
+ logExcerpt.append(System.lineSeparator());
+ logExcerpt.append(lineFromFile);
+ logExcerpt.append(System.lineSeparator());
+ // extract potential stack trace from log
+ while (scanner.hasNextLine()) {
+ String line = scanner.nextLine();
+ if (!line.isEmpty() && (Character.isWhitespace(line.charAt(0)) || line.startsWith("Caused by"))) {
+ logExcerpt.append(line);
+ logExcerpt.append(System.lineSeparator());
+ } else {
+ break;
+ }
+ }
+ prohibitedExcerpts.add(logExcerpt.toString());
+
  return true;
  }
  }
@@ -355,7 +375,9 @@ public boolean accept(File dir, String name) {
  while (scanner.hasNextLine()) {
  LOG.warn("LINE: " + scanner.nextLine());
  }
- Assert.fail("Found a file " + foundFile + " with a prohibited string: " + Arrays.toString(prohibited));
+ Assert.fail(
+ "Found a file " + foundFile + " with a prohibited string (one of " + Arrays.toString(prohibited) + "). " +
+ "Excerpts:" + System.lineSeparator() + prohibitedExcerpts);
  }
  }