I can\'t get Keras to predict anything. Not even in this minimalistic model:
from keras.models import Sequential
from keras.layers import Dense
import numpy as np
I pasted your code into https://colab.research.google.com and it didn't give me an error. (python2)
I did however get a warning about int to float conversion.
I would try to specify the test_input dtype explicitly as in:
test_input = np.zeros((1,inDim), dtype=float)
Since that seems to be the error message that is being output.