Added instructions append for error handling and updated JinJa2 template and regenerated test file.

Author: BethanyG

exercises/practice/variable-length-quantity/.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` if the sequence to decode or encode is incomplete. 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
+# if the sequence is incomplete
+raise ValueError("incomplete sequence")
+```

exercises/practice/variable-length-quantity/.meta/example.py

@@ -29,6 +29,6 @@ def decode(bytes_):
             values.append(n)
             n = 0
         elif i == len(bytes_) - 1:
-            raise ValueError('incomplete byte sequence')
+            raise ValueError("incomplete sequence")
 
     return values

exercises/practice/variable-length-quantity/.meta/template.j2

@@ -15,13 +15,13 @@ class {{ exercise | camel_case }}Test(unittest.TestCase):
         {%- for sub_case in case.cases %}
     def test_{{ sub_case["description"] | to_snake }}(self):
         {%- if sub_case is error_case %}
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             {{ sub_case["property"] }}({{ list_int_to_hex(sub_case["input"]["integers"]) }})
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "{{ sub_case["expected"]["error"] }}")
         {%- else %}
         self.assertEqual({{ sub_case["property"] }}({{ list_int_to_hex(sub_case["input"]["integers"]) }}), {{ list_int_to_hex(sub_case["expected"]) }})
         {%- endif %}
         {% endfor -%}
 
     {% endfor %}
-
-{{ macros.footer() }}

exercises/practice/variable-length-quantity/variable_length_quantity_test.py

@@ -100,12 +100,16 @@ def test_maximum_32_bit_integer(self):
         self.assertEqual(decode([0x8F, 0xFF, 0xFF, 0xFF, 0x7F]), [0xFFFFFFFF])
 
     def test_incomplete_sequence_causes_error(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             decode([0xFF])
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "incomplete sequence")
 
     def test_incomplete_sequence_causes_error_even_if_value_is_zero(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             decode([0x80])
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "incomplete sequence")
 
     def test_multiple_values(self):
         self.assertEqual(
@@ -130,11 +134,3 @@ def test_multiple_values(self):
             ),
             [0x2000, 0x123456, 0xFFFFFFF, 0x0, 0x3FFF, 0x4000],
         )
-
-    # Utility functions
-    def assertRaisesWithMessage(self, exception):
-        return self.assertRaisesRegex(exception, r".+")
-
-
-if __name__ == "__main__":
-    unittest.main()