Working on Bittrex implementation and unit tests

catalyst/exchange/exchange_errors.py

@@ -69,9 +69,9 @@ class InvalidSymbolError(ZiplineError):
     ).strip()
 
 
-class InvalidOrderType(ZiplineError):
+class InvalidOrderStyle(ZiplineError):
     msg = (
-        'Order type not found.'
+        'Order style {style} not supported by exchange {exchange}.'
     ).strip()
 
 
@@ -79,3 +79,10 @@ class SidHashError(ZiplineError):
     msg = (
         'Unable to hash sid from symbol {symbol}.'
     ).strip()
+
+
+class MismatchingBaseCurrencies(ZiplineError):
+    msg = (
+        'Unable to trade with base currency {base_currency} when the '
+        'algorithm uses {algo_currency}.'
+    ).strip()