implement exercise spiral-matrix closes exercism#752

exercises/spiral-matrix/README.md

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+# Spiral Matrix
+
+Given the size, return a square matrix of numbers in spiral order.
+
+The matrix should be filled with natural numbers, starting from 1
+in the top-left corner, increasing in an inward, clockwise spiral order,
+like these examples:
+
+###### Spiral matrix of size 3
+
+```text
+1 2 3
+8 9 4
+7 6 5
+```
+
+###### Spiral matrix of size 4
+
+```text
+ 1  2  3 4
+12 13 14 5
+11 16 15 6
+10  9  8 7
+```
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
+
+For example, if you're submitting `bob.py` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/python/bob/bob.py`.
+
+For more detailed information about running tests, code style and linting,
+please see the [help page](http://exercism.io/languages/python).
+
+## Source
+
+Reddit r/dailyprogrammer challenge #320 [Easy] Spiral Ascension. [https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/](https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/spiral-matrix/spiral_matrix.py

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+def matrix(num):
+    pass

exercises/spiral-matrix/spiral_matrix_test.py

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+import unittest
+
+from spiral_matrix import matrix
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.0.0
+
+class SpiralMatrixTests(unittest.TestCase):
+    def test_empty_spiral(self):
+        expected = []
+        self.assertEqual(matrix(0),expected)
+
+    def test_trivial_spiral(self):
+        expected = [[1]]
+        self.assertEqual(matrix(1),expected)
+
+    def test_spiral_size_2(self):
+        expected = [[1,2],
+                    [4,3]]
+        self.assertEqual(matrix(2),expected)
+
+    def test_spiral_size_3(self):
+        expected = [[1,2,3],
+                    [8,9,4],
+                    [7,6,5]]
+        self.assertEqual(matrix(3),expected)
+
+    def test_spiral_size_4(self):
+        expected = [[1,2,3,4],
+                    [12,13,14,5],
+                    [11,16,15,6],
+                    [10, 9, 8,7]]
+        self.assertEqual(matrix(4),expected)
+
+    def test_spiral_size_5(self):
+        expected = [[1,2,3,4,5],
+                    [16,17,18,19,6],
+                    [15,24,25,20,7],
+                    [14,23,22,21,8],
+                    [13,12,11,10,9]]
+        self.assertEqual(matrix(5),expected)
+
+if __name__ == '__main__':
+    unittest.main()