added unit test example / lesson

a unit testing example -- starter code.

Author: PythonCHB

Sources/code/test_sum_13.py

@@ -0,0 +1,148 @@
+"""
+
+Test driven development:
+
+
+Example from Coding Bat: List-2 > sum13
+
+https://codingbat.com/prob/p167025
+
+Return the sum of the numbers in the array, returning 0 for an empty array. Except the number 13 is very unlucky, so it does not count and numbers that come immediately after a 13 also do not count.
+
+
+sum13([1, 2, 2, 1]) → 6
+sum13([1, 1]) → 2
+sum13([1, 2, 2, 1, 13]) → 6
+sum13([1, 2, 2, 1]) → 6
+sum13([1, 1]) → 2
+sum13([1, 2, 2, 1, 13]) → 6
+sum13([1, 2, 13, 2, 1, 13]) → 4
+sum13([13, 1, 2, 13, 2, 1, 13]) → 3
+sum13([]) → 0
+sum13([13]) → 0
+sum13([13, 13]) → 0
+sum13([13, 0, 13]) → 0
+sum13([13, 1, 13]) → 0
+sum13([5, 7, 2]) → 14
+sum13([5, 13, 2]) → 5
+sum13([0]) → 0
+sum13([13, 0]) → 0 
+"""
+
+import pytest
+
+# def sum13(nums):
+#     """
+#     non-functional -- but the tests will run (and fail)
+#     """
+#     return None
+
+# def sum13(nums):
+#     """
+#     simple sum -- no special handling of 13 -- should pass some tests.
+#     """
+#     return sum(nums)
+
+
+# def sum13(nums):
+#     """
+#     using a comprehension to filter out the 13s
+
+#     - more tests should pass, but not all.
+#     """
+#     return sum(n for n in nums if n!=13)
+
+
+# def sum13(nums):
+#     """
+#     darn -- comprehension can't handle the "after a 13" case
+
+#     do it from scratch with  while loop
+
+#     fails the two 13s in a row test!
+#     """
+#     total = 0
+#     i = 0
+#     while i < len(nums):
+#         if nums[i] != 13:
+#             total += nums[i]
+#         else:
+#             i += 1
+#         i += 1
+#     return total
+
+
+# def sum13(nums):
+#     """
+#     Use a for loop, and keep track of the previous 13
+
+#     passes all tests!
+#     """
+#     print(nums)
+#     total = 0
+#     prev_13 = False
+#     for i, n in enumerate(nums):
+#         if n == 13:
+#             prev_13 = True
+#             continue
+#         elif prev_13:
+#             prev_13 = False
+#             continue
+#         else:
+#             total += n
+#     return total
+
+
+def sum13(nums):
+    """
+    Use the iterator protocol -- nifty? but not any simpler really.
+
+    Fails for repeated 13 in middle
+
+    Works with any iterable, so that's nice.
+    """
+    total = 0
+    nums_i = iter(nums)
+    for n in nums_i:
+        if n != 13:
+            total += n
+        else:
+            try:
+                next(nums_i)
+            # this is necessary for the case where there's a 13 at the end.
+            except StopIteration:
+                break
+    return total
+
+# Using the nifty pytest.parametrize, so we only have to write one test
+
+test_data = [
+    ([1, 2, 2, 1], 6),
+    ([1, 1], 2),
+    ([1, 2, 2, 1, 13], 6),
+    ([1, 2, 2, 1], 6),
+    ([1, 1], 2),
+    ([1, 2, 2, 1, 13], 6),
+    ([1, 2, 13, 2, 1, 13], 4),
+    ([13, 1, 2, 13, 2, 1, 13], 3),
+    ([], 0),
+    ([13], 0),
+    ([13, 13], 0),
+    ([13, 0, 13], 0),
+    ([13, 1, 13], 0),
+    ([5, 7, 2], 14),
+    ([5, 13, 2], 5),
+    ([0], 0),
+    ([13, 0], 0),
+    # These are not part of original test suite
+    # ([3, 13, 13, 2, 5], 8),
+    # (iter([13, 1, 2, 13, 2, 1, 13]), 3), #  Does it work with an iterable?
+    ]
+
+@pytest.mark.parametrize('nums, result', test_data)
+def test_sum13(nums, result):
+    assert sum13(nums) == result
+
+
+
+