How to get names of all classes in a dataset generated by ImageDataGenerator ? 

By using ImageDataGenerator.class_indices attribute

classlabels = test_ds_gen.class_indices

print(classlabels)

print(classlabels.keys())

{'daisy': 0, 'dandelion': 1, 'roses': 2, 'sunflowers': 3, 'tulips': 4}

dict_keys(['daisy', 'dandelion', 'roses', 'sunflowers', 'tulips'])