Added instructions append for error handling, updated JinJa2 template and example, and regenerated test files.

Author: BethanyG

exercises/practice/grains/.docs/instructions.append.md

@@ -0,0 +1,14 @@
+# Instructions append
+
+## Exception messages
+
+Sometimes it is necessary to [raise an exception](https://docs.python.org/3/tutorial/errors.html#raising-exceptions). When you do this, you should always include a **meaningful error message** to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. For situations where you know that the error source will be a certain type, you can choose to raise one of the [built in error types](https://docs.python.org/3/library/exceptions.html#base-classes), but should still include a meaningful message.
+
+This particular exercise requires that you use the [raise statement](https://docs.python.org/3/reference/simple_stmts.html#the-raise-statement) to "throw" a `ValueError` when the square input is out of range. The tests will only pass if you both `raise` the `exception` and include a message with it.
+
+To raise a `ValueError` with a message, write the message as an argument to the `exception` type:
+
+```python
+# when the square value is not in the acceptable range        
+raise ValueError("square must be between 1 and 64")
+```

exercises/practice/grains/.meta/example.py

@@ -1,10 +1,10 @@
 def square(number):
     if number == 0:
-        raise ValueError("Square input of zero is invalid.")
+        raise ValueError("square must be between 1 and 64")
     elif number < 0:
-        raise ValueError("Negative square input is invalid.")
+        raise ValueError("square must be between 1 and 64")
     elif number > 64:
-        raise ValueError("Square input greater than 64 is invalid.")
+        raise ValueError("square must be between 1 and 64")
 
     return 2 ** (number - 1)
 

exercises/practice/grains/.meta/template.j2

@@ -2,10 +2,14 @@
 
 {% macro test_case(case) %}
     {%- set input = case["input"] %}
+    {%- set expected = case["expected"] %}
+    {%- set exp_error = expected["error"]  %}
     def test_{{ case["description"] | to_snake }}(self):
     {%- if case is error_case %}
-          with self.assertRaisesWithMessage(ValueError):
-                {{ case["property"] | to_snake }}({{ input["square"] }})
+        with self.assertRaises(ValueError) as err:
+            {{ case["property"] | to_snake }}({{ input["square"] }})
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "{{ exp_error }}")
     {%- else%}
           self.assertEqual({{ case["property"] | to_snake }}(
             {{ input["square"] }}), {{ case["expected"] }})
@@ -23,6 +27,4 @@ class {{ exercise | camel_case }}Test(unittest.TestCase):
         {%-else%}
         {{test_case(case)}}
         {%-endif%}
-    {% endfor %}
-
-{{ macros.footer(has_error_case) }}
+    {% endfor %}

exercises/practice/grains/grains_test.py

@@ -31,24 +31,22 @@ def test_grains_on_square_64(self):
         self.assertEqual(square(64), 9223372036854775808)
 
     def test_square_0_raises_an_exception(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             square(0)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
 
     def test_negative_square_raises_an_exception(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             square(-1)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
 
     def test_square_greater_than_64_raises_an_exception(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             square(65)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
 
     def test_returns_the_total_number_of_grains_on_the_board(self):
         self.assertEqual(total(), 18446744073709551615)
-
-    # Utility functions
-    def assertRaisesWithMessage(self, exception):
-        return self.assertRaisesRegex(exception, r".+")
-
-
-if __name__ == "__main__":
-    unittest.main()