Merge pull request #814 from Vlatombe/delete-diagnostics

Improve exception readability in case a directory can't be deleted because it still contains files

src/main/java/org/jvnet/hudson/test/TemporaryDirectoryAllocator.java

@@ -36,6 +36,7 @@
 import java.util.logging.Logger;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import org.apache.commons.lang.StringUtils;
 
 /**
  * Allocates temporary directories and cleans it up at the end.
@@ -140,9 +141,11 @@ private void delete(Path p) throws IOException {
             }
             Files.deleteIfExists(p);
         } catch (DirectoryNotEmptyException x) {
+            String pathString = p.toString();
             try (Stream<Path> children = Files.list(p)) {
-                throw new IOException(children.map(Path::toString).collect(Collectors.joining(" ")), x);
+                x.addSuppressed(new IOException("These files still exist : " + children.map(Path::toString).map(s -> StringUtils.removeStart(s, pathString + File.separator)).collect(Collectors.joining(", "))));
             }
+            throw x;
         }
     }