title: Test data gives "Found 0 images in 0 classes" using flow_from_directory
body: <p>This is my flow_from_directory code</p>
  <pre><code>train_image_generator = ImageDataGenerator(rescale=1./255)
  validation_image_generator = ImageDataGenerator(rescale=1./255)
  test_image_generator = ImageDataGenerator(rescale=1./255)
  
  train_data_gen = train_image_generator.flow_from_directory(
          train_dir,
          target_size=(150, 150),
          batch_size=batch_size,
          class_mode='binary')
  val_data_gen =validation_image_generator.flow_from_directory(
          validation_dir,
          target_size=(150, 150),
          batch_size=batch_size,
          class_mode='binary')
  test_data_gen = test_image_generator.flow_from_directory(
          test_dir,
          target_size=(150, 150),
          batch_size=batch_size,
          class_mode='binary',
          shuffle = False,)
  </code></pre>
  <p>And it prints:</p>
  <p>Found 2000 images belonging to 2 classes.
  Found 1000 images belonging to 2 classes.
  Found 0 images belonging to 0 classes.</p>
  <p>Even though the data exists as I used:</p>
  <p><code>!ls  /root/.keras/datasets/cats_and_dogs/test</code></p>
  <p>Which gives the output:</p>
  <pre><code>10.jpg  15.jpg  1.jpg   24.jpg  29.jpg  33.jpg  38.jpg  42.jpg  47.jpg  5.jpg
  11.jpg  16.jpg  20.jpg  25.jpg  2.jpg   34.jpg  39.jpg  43.jpg  48.jpg  6.jpg
  12.jpg  17.jpg  21.jpg  26.jpg  30.jpg  35.jpg  3.jpg   44.jpg  49.jpg  7.jpg
  13.jpg  18.jpg  22.jpg  27.jpg  31.jpg  36.jpg  40.jpg  45.jpg  4.jpg   8.jpg
  14.jpg  19.jpg  23.jpg  28.jpg  32.jpg  37.jpg  41.jpg  46.jpg  50.jpg  9.jpg
  </code></pre>
  <p><strong>what am I doing wrong or what must be Done?</strong></p>