Bugs in filters_test.py

[WindQAQ]

In image/filters_test.py, there are some buggy test cases:

1. There are some patterns like
   

   addons/tensorflow_addons/image/filters_test.py

   Lines 60 to 63 in 6bb0d4b

   	with self.assertRaisesRegexp(TypeError,
   	'Size of the filter must be Integers'):
   	median_filter2d(tf_img, (3.5, 3))
   	median_filter2d(tf_img, (None, 3))

   
   However, this is not safe because each context manager will catch only one exception, and then exit. That it, the following code snippet will pass the test:

def foo(x):
    if x < 5:
        raise ValueError("fail " + str(x))


class Test(tf.test.TestCase):

    def test_context_manager(self):
        with self.assertRaisesRegexp(ValueError, "fail 3"):
            foo(3)
            foo(2)
            foo(1)

        with self.assertRaises(ValueError):
            foo(5)
            foo(4)
            foo(3)

2. One test case disables eager execution, but this will affect all test cases (in the same file) executed after it.
   

   addons/tensorflow_addons/image/filters_test.py

   Lines 71 to 75 in 6bb0d4b

   	def test_dimension(self):
   	tf.compat.v1.disable_eager_execution()
   	tf_img = tf.compat.v1.placeholder(tf.int32, shape=[3, 4, None])
   	tf_img1 = tf.compat.v1.placeholder(tf.int32, shape=[3, None, 4])
   	tf_img2 = tf.compat.v1.placeholder(tf.int32, shape=[None, 3, 4])

   
   In other words, test_check_eager will fail in this toy test case.

class Test(tf.test.TestCase):

    # Make it execute first
    def test_a(self):
        tf.compat.v1.disable_eager_execution()
        tf.compat.v1.placeholder(tf.float32, shape=(1, 2, None))

    def test_check_eager(self):
        if not tf.executing_eagerly():
            raise Exception("Not in eager mode")

This might not be what we want. In order to utilize tf.compat.v1.placeholder, which can be used to test None shape, in tf2.0, maybe @run_deprecated_v1 is helpful enough.

[facaiy]

Tzu-Wei, would you like to fix them?