calc: test even more edge cases

These additional cases (and a new error handler) cover as much of the
`tools.calculation` submodule as possible using the example decorator.
Further coverage of `tools.calculation` would require real unit tests
of the sort one finds in this project's `test/` directory.

sopel/modules/calc.py

@@ -16,9 +16,19 @@
 @plugin.example('.c foo * bar', "Can't process expression: Node type 'Name' is not supported.")
 @plugin.example('.c 10 / 0', 'Division by zero is not supported in this universe.')
 @plugin.example('.c 10\\2', 'Invalid syntax')
+@plugin.example('.c (10**1000000)**2',
+                "Couldn't run the calculation: "
+                "ValueError('Pow expression too complex to calculate.')")
+@plugin.example('.c (10**100000)**2 * (10**100000)**2',
+                "Couldn't run the calculation: "
+                "ValueError('Value is too large to be handled in limited time and memory.')")
 @plugin.example('.c 5 + 3', '8')
 @plugin.example('.c 0.9*10', '9')
 @plugin.example('.c 10*0.9', '9')
+@plugin.example('.c 0.5**2', '0.25')
+@plugin.example('.c 3**0', '1')
+@plugin.example('.c 0 * 5', '0')
+@plugin.example('.c 5**5', '3125')
 @plugin.example('.c 2*(1+2)*3', '18', user_help=True)
 @plugin.example('.c 2**10', '1024', user_help=True)
 @plugin.example('.c 5 // 2', '2', user_help=True)
@@ -43,5 +53,8 @@ def c(bot, trigger):
     except SyntaxError:
         bot.reply('Invalid syntax')
         return
+    except ValueError as err:
+        bot.reply("Couldn't run the calculation: %r" % err)
+        return
 
     bot.say(result)