fix (hopefully) test flakiness

src/test/java/ysoserial/payloads/FileUploadTest.java

@@ -47,9 +47,12 @@ public class FileUploadTest implements CustomTest {
             payload.call();
 
             File found = null;
-            for ( File f : this.repo.listFiles()) {
-                found = f;
-                break;
+            for (int i = 0; i < 50 && found == null; i++) { // try for 5s before failing
+                for (File f : this.repo.listFiles()) {
+                    found = f;
+                    break;
+                }
+                Thread.sleep(100);
             }
             Assert.assertNotNull("File not copied", found);
             if (OS.get() != OS.WINDOWS) {
@@ -60,11 +63,21 @@ public class FileUploadTest implements CustomTest {
         } finally {
             if ( this.repo.exists()) {
                 for ( File f : this.repo.listFiles()) {
-                    f.deleteOnExit();
+                    safeDeleteOnExit(f);
                 }
-                this.repo.deleteOnExit();
+                safeDeleteOnExit(this.repo);
             }
-            this.source.deleteOnExit();
+            safeDeleteOnExit(this.source);
+        }
+    }
+
+    private static void safeDeleteOnExit(File f) {
+        try {
+            if (f.exists()) {
+                f.deleteOnExit();
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
         }
     }