ENH: Added test cases to ensure the behavior of integer as it is.

There is a need to add test case which ensure and maintain the behavior of integer. As per pr #3567, which speed up integer scalar's operations by avoiding the conversion of integer to NumPy Scalar.


Test case
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<b>For np.int16</b>
<pre>
a = np.array([2**15-1]], dtype=np.int16)
b = np.array([-2**15], dtype=np.int16)           
assert_equal(a,b-1)
</pre>

<b>For np.uint16</b>
<pre>
a = np.array([2**16-1]], dtype=np.uint16)
b = np.array([0], dtype=np.uint16)           
assert_equal(a+1,b)
</pre>